Glossary of Oilfield Terms

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Oilfield Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Nomenclature

ABANDON- To cease efforts to produce oil or gas from a well, and to plug a depleted formation and salvage all material and equipment.

ABSOLUTE PERMEABILITY- The proportionality constant in D’Arcy’s flow equation; a measure of the ease with which a fluid will flow through a porous medium.

ABSOLUTE VOLUME- The volume per unit mass, reciprocal of absolute density.

ABSORB- To accumulate or “drink in,” as a liquid into a porous solid, or a gas into a liquid. A sponge absorbs water. We pump fluid into a fractured formation and the fluid leaks off to the matrix permeability. The formation absorbs the leak-off fluid.

ABSORPTION- The penetration or apparent disappearance of molecules or ions of one or more substances into the interior of a solid or liquid. For example, in hydrated bentonite, the planar water that is held between the mica-like layers is the result of absorption.

ABYSSAL- Refers to the great depths of seas or lakes where light is absent. Greater than 6000 feet of water.

ACID- Any chemical compound containing hydrogen capable of being replaced by positive elements or radicals to form salts. In terms of the dissociation theory, it is a compound that, on dissociation in solution, yields excess hydrogen ions. Acids lower the pH. Examples of acids or acidic substances are: hydrochloric acid, tannic acid, sodium acid pyrophosphate. A substance whose molecules ionize in a water solution to release the hydrogen ion from the constituent element. The strength of an acid is proportional to the concentration of hydrogen ions present.

ACID RESISTANCE- The ability of a hardened cement slurry to withstand the softening and corrosive effects of organic or mineral acids, or water solutions of these acids and their salts having a pH lower than 7.0.

ACIDITY- The relative acid strength of liquids as measured by pH. A pH value below 7. See pH.

ACIDIZING- The practice of applying acids to the walls of oils and gas wells to remove any material which obstructs the entrance of fluids. Also used in carbonate formations, such as limestone, to increase porosity.

ADAPTER- A device to provide connection between two other parts.

ADDITIVE- A material other than cement and water which is added to a cement subsequent to its manufacture to modify its properties.

Glossary of Oilfield Terms

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ADHESION- The force which holds together unlike molecules.

ADMIX- To add one material to another by mixing. NOTE: Admix should not be used replaceably with additive.

ADSORB- The adhesion, in an extremely thin layer, of the molecules of a gas, a liquid or of dissolved substances on the surface of that which it is in contact. Generally, adsorption takes place on the surface of liquids or solids. Think of this like a paint film a few millionths of an inch thick. Our NE compounds adsorb on the face of a fracture in a formation. One theory about the action of scale inhibitors is that they are adsorbed on the face of the fracture. The molecules of the inhibitor are then slowly desorbed from the surface of the rock by the flow of produced fluids. The molecules of an emulsifier are adsorbed in a microscopic film on the surface of tiny globules of acid, holding them in the shape of a ball, and permitting them to be suspended in diesel oil or kerosene. This is emulsified acid. The same mechanism is responsible for the creation of unwanted emulsions of treating fluids with formation fluids.

ADSORPTION- A surface phenomenon exhibited by a solid (adsorbent) to hold or concentrate gases, liquids, or dissolved substances (adsorptive) upon its surface, a property due to adhesion. For example, that water held to the outside surface of hydrated bentonite is adsorbed water. The accumulation of a thin layer of molecules of gas or liquid on a solid surface.

AEOLIAN- An adjective applied to rocks formed of wind-borne sands.

AERATE- Intimately admixing water and air.

AERATION- The technique of injecting air or gas in varying amounts into a drilling fluid for the purpose of reducing hydrostatic head. Compare Air Cutting.

AEROBIC- Bacteria that are active only in the presence of oxygen. Bacteria which requires free oxygen to degrade organic material.

AGING- Natural or artificial maturing of cement, cement slurries, and hardened cement paste during which various physio-chemical changes take place.

AGGLOMERATE- The larger groups of individual particles usually originating in sieving or drying operations.

AGGLOMERATION- The grouping of individual particles.

AGGREGATE- A group of two or more individual particles held together by strong forces. Aggregates are stable to normal stirring, shaking, or handling as powder or a suspension. They may be broken by drastic treatment such as ball milling a powder or by shearing a suspension. An essentially inert material of mineral origin having a particle size predominantly greater than 100 mesh, which forms a mortar or concrete when bound together with hardened cement paste.

AGGREGATION- Formation of aggregates. In drilling fluids, aggregation results in the stacking of the clay platelets face to face. The viscosity and gel strength decrease in consequence.


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AIR CUTTING- The inadvertent mechanical incorporation and dispersion of air into a drilling-fluid system. Compare Aeration.

AIR/GAS LIFT- Lifting of liquids by injection, directly into the well, of air or gas.

AIR/OIL RATIO- The quantity of air required for injection to burn and displace a unit volume of oil in the in-situ combustion process.

ALGAE- Cellular aquatic plants, mostly of marine habitat. They are found fossil, more or less, in every formation from the Pre-Cambrian to Recent.

ALGAL- Pertaining to algae.

ALIPHATIC- Those hydrocarbons which have straight or branched carbon chains in their molecular structure. The greater portions of the hydrocarbons in the crude oil are aliphatic in nature. Kerosene, diesel oil and gasoline are all mixtures of aliphatic or straight chain hydrocarbons.

ALKALI- Any compound having marked basic properties. See Base. In chemistry, any substance having marked basic properties. In its restricted an common sense, the term is applied only to hydroxides of potassium, sodium, lithium, and ammonium.

ALKALI FLATA- sterile plain, containing an excess of alkali, at the bottom of an undrained basin in an arid region. A playa.

ALKALINITY- The combining power of a base measured by the maximum number of equivalents of an acid with which it can react to form a salt. In water analysis, it represents the carbonates, bi-carbonates, hydroxides, and occasionally the borates, silicates, and phosphates in the water. It is determined by titration with standard acid to certain datum points. See API RP 13B* for specific directions for determination of phenolphthalein (Pf) and methyl orange (Mf) alkalinities of the filtrate in drilling fluids and the alkalinity of mud itself (Pm). Also see Pf, Mf, and Pm.

- *Standard Procedure for Testing Drilling Fluids, American

- Petroleum Institute, Dallas, Texas, Nov. (1962) 1st Ed.

ALLOCHTHONUS- Referring to limestone formed by the accumulation of transported organic matter or calcareous fragments, rhombs, colites, etc.

ALLOGENIC- Originating elsewhere. The contrasted form is authigenic.

ALLOWABLE- The amount of oil or gas that a well is permitted by state authorities to produce during a given period.

ALLUVIAL- An adjective denoting that which is transported by running water.

ALLUVIAL FAN- Sediments deposited by a swift stream flowing out onto a valley floor from higher land.

ALUMINUM STEARATE- An aluminum salt of stearic acid used as a defoamer. See Stearate.


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AMBER- A hard, brittle, translucent, fossilized vegetal resin, of a clear yellowish-brown or light-yellow color.

AMBIENT- We use this term to describe temperature. Strictly speaking, the term is defined as “completely surrounding.” Ambient temperature, then would be the temperature of the air surrounding us. We stretch this definition a little and refer to pumping fluids at ambient temperature. We mean we don’t heat or cool the fluid, but use it just like it is in the tank. Defined as “completely surrounding,” strictly speaking. Ambient temperature, then, would be the temperature of the air surrounding us. We stretch this definition a little and refer to pumping fluids at ambient temperature. We mean that we do not heat or cool the fluid, but use it at the temperature is in the tank.

AMORPHOUS- Without form; applied to rocks and minerals having no definite crystalline structure.

AMPHOTERIC- Anionic or cationic depending on outside conditions, pH for example.

ANAEROBIC- Bacteria that do not require free oxygen to thrive.

ANALYSIS, CORE- Laboratory examination of geological samples taken from the well bore. This examination is used to determine the capacity of the formation to contain oil and gas, the possibility of oil and gas passing through the formation, the degree of saturation of the formation with oil, gas, and water, and for other purposes.

ANALYSIS, MUD OR DRILLING FLUID- Examination and testing of the drilling fluid to determine its physical and chemical properties and condition.

ANDESITE- A very hard granite rock composed of granular feldspar.

ANGULAR UNCONFORMITY- An uncomformity in which the beds below the unconformable contact had undergone movement and erosion before the upper beds were deposited. The lower beds are, therefore, not parallel to those above.

ANHYDRITE- See Calcium Sulfate. Anhydrite is often encountered while drilling. It may occur as thin stringers or massive formations. CaSO4.

ANHYDROUS- Without water. Destitute of water, especially water of crystallization.

ANILINE POINT- The lowest temperature at which equal volumes of freshly distilled aniline and an oil that is being tested are completely miscible. This test gives an indication of the character (paraffinic, naphthenic, asphaltic, aromatic, mid-continent, etc.) of the oil. The aniline point of diesels or crudes used in drilling mud is also an indication of the deteriorating effect these materials may have on natural or synthetic rubber. The lower the aniline point of an oil the more severe it usually is in damaging rubber parts.

ANION- A negatively charged atom or radical, such as C1-, OH-, So4=, etc., in

solution of an electrolyte. Anions move toward the anode (positive electrode) under the influence of an electrical potential.


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ANIONIC- Refers to any anion (atom or chemical group bearing a negative electrical charge). It is used specifically to describe certain surfactants. An anionic surfactant ionizes to produce a cation (positively charged) ion which is usually a metallic ion such as sodium. When a cation is produced through ionization, an anion must also be produced. In this case, the anion is composed of the large organic portion of the molecule. The sodium is always attached to the water soluble end of the surfactant molecule, so when the sodium splits off in ionization, the water soluble end is left with a negative charge. Sand grains have a negative charge, so when an anionic surfactant is adsorbed on the sand grain surface, the two negative charges repel each other and the oil soluble end of the anion is adsorbed on the sand, leaving the negatively charged (water soluble) end sticking out. The sand grain is now said to be water wet. Limestone and dolomite have a positive charge. When an anionic surfactant adsorbs on these surfaces, the negatively charged (water soluble) end is attached to the surface, leaving the oil soluble end sticking out. The limestone or dolomite is now said to be oil wet. Most anionic surfactants will leave sandstone water wet, and limestone or dolomite will be oil wet.

ANISOTROPIC- Not having the same properties in all directions.

ANNULAR VELOCITY- The velocity of a fluid moving in the annulus.

ANNULUS, ANNULAR SPACE- Any space in a well bounded by two or more circular surfaces, one of which is concave. This would include single or multiple strings of tubing in a hole or casing.

ANNULUS (ANNULAR SPACE)- The space surrounding pipe suspended in the well bore. The outer wall of the annulus may be an open hole or it may be larger pipe.

ANNULUS OR ANNULAR SPACE- The space between the drill string and the wall of the hole or casing.

ANOMALY- Deviation from the common rule; irregularity.

ANTHRACITE- A hard black lustrous coat containing 85 to 95% carbon as against 70 to 85% in bituminous or soft coal.

ANTICLINAL LINE OR AXIS- The medial line of a folded structure from which the strata dip on either side.

ANTICLINE- A fold that is convex upward or, in more complicated folds, is inferred to have had such an attitude at some stage of its development.

ANTIFOAM- A substance used to prevent foam by greatly decreasing the surface tension. Compare Defoamer.

APHANITIC- Denoting a rock with grains so minute or amorphous as to be unidentifiable.

API- American Petroleum Institute. Headquarters of the API Division of Production are at 300 Corrigan Tower Bldg., Dallas, Texas.


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API CEMENT CLASSES- A classification system for oil well cements defined in API Std 10A.

API GRAVITY- The gravity (weight per unit volume) of crude oil or other related fluids as measured by a system recommended by the American Petroleum Institute. It is related to specific gravity by the following formula:

Deg API = 141.5_- 131.5

sp gr 60°F/60°F

Gravity (weight per unit of volume) of crude oil as measured by a system recommended by the API. A standard measure related to crude oil density (See Summary of Equations).

APPARENT VISCOSITY- The viscosity a fluid appears to have on a given instrument at a stated rate of shear. It is a function of the plastic viscosity and the yield point. The apparent viscosity in centipoises, as determined by the direct-indicating viscometer (which see), is equal to 1/2 the 600-rpm reading. See also Viscosity, Plastic Viscosity and Yield Point. In a Newtonian fluid, the apparent viscosity is numerically equal to the plastic viscosity.

APRON RING- The first or lowest ring of plates in a tank.

APRON SPREADER- A flat plate in the bottom of a gunbarrel tank that causes fluid coming into the tank to spread out.

AQUEOUS- Used to describe fluids prepared from water. Usually used to distinguish from hydrocarbon fluids. An aqueous fluid may be plain fresh water, or it may have a great number of additives, which give it properties much different from plain water. Examples are salt water of various weights, HCL, KCL water, formic and acetic acids.

AQUIFER- Ground stratum which bears water in recoverable quantity.

ARCUATE- Denoting a delta with a large flooding plain and transient drainage channels.

AREAL SWEEP EFFICIENCY- The fraction of the area of an injection/production well pattern swept out by the injected fluid.

ARENACEOUS- Having a sand content or sandy nature.

ARGILLACEOUS- Having a clay or shale content or component.

ARKOSIC- Associated with arkose, a sandstone with 25% or more feldspar.

AROMATIC- Describes those hydrocarbons that have carbon chains bent and connected to form a ring or cycle. Aromatic hydrocarbons are sometimes called “cyclic” hydrocarbons. Many of these compounds, as the name implies, have a fragrant or spicy odor. Xylene bottoms is a mixture of aromatic compounds including xylene, benzene and toluene. A solid aromatic hydrocarbon which is commonly used is napthalene or mothballs.


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ASBESTOS- Term applied to many fibrous silicate minerals, some forms of which are used in certain drilling fluids.

ASPHALT- A natural or mechanical mixture of solid or viscous bitumens found in natural beds or obtained as a residue from petroleum. Asphalt, blends containing asphalt, and altered asphaltic materials (e.g., air-blown, chemically modified, etc.) have been added to certain drilling fluids for such widely different purposes as a component in oil-base muds, lost-circulation material, emulsifier, fluid-loss-control agent, wall-plastering agent, etc.

ASPHALTIC MATERIALS- One of a group of solid, liquid, or semi-solid materials, predominantly mixtures of hydrocarbons and their non-metallic derivatives, obtained either from natural bituminous deposits, or from the residue of petroleum refining.

ATOLL- A ring-shaped reef enclosing a circular lagoon.

ATOM- According to the atomic theory, the smallest quantity of an element that is capable of entering into chemical combination or that can exist alone.

ATOMIC NUMBER- The relative weight of an atom of an element as compared with the weight of 1 atom of oxygen, using 16 as the weight of 1 atom of oxygen.

ATTAPULGITE CLAY- A colloidal, viscosity-building clay used principally in salt-water muds. Attapulgite, a special fullers earth, is a hydrous magnesium aluminum silicate.

AULACOGEN- A deep depositional through at right angles to a re-entrant fold belt.

AUTHIGENIC- A term meaning generated on the spot, applied to those constituents that came into existence with or after the formation of the rock of which they constitute a pare; e.g., the primary and secondary minerals of igneous rocks, and the cements of sedimentary rocks.

AUTOCHTHONUS- Referring to a limestone formed by the in-place accumulation of organic remains or directly by carbonate precipitation.

AUTOCLAVE EXPANSION- A measurement or test made as provided in ASTM C 151: Test for Autoclave Expansion of Portland Cement. See Soundness.

BABBITT- Soft, easily melted metal used for bearings.

BACK-OFF- To unscrew.

BACK PRESSURE- The pressure resulting from restriction of full natural flow of oil or gas.

BACK-UP MAN- The person who holds one length of pipe while another length is being screwed into or out of it.

BACTERIA- The simplest form of animal life.

BACTERICIDE- An agent capable of destroying bacteria.


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BAFFLES- Plates which change the direction of flow of fluids.

BALANCE, MUD- A beam-type balance used in determining mud density. It consists primarily of a base, graduated beam with constant-volume cup, lid, rider, knife edge, and counterweight.

BALL AND SEAT- The main parts of the valves in a plunger-type oil-well pump.

BAR- A bank of sand, gravel, or other material, especially at the mouth of a river or harbor.

BARCHAN- A crescent-shaped sand dune, convex windward.

BARITE, BARYTES, OR HEAVY SPAR- Natural barium sulfate used for increasing the density of drilling fluids. If required, it is usually upgraded to a specific gravity of 4.20. The barite mineral occurs in white, grayish, greenish, and reddish ores or crystalline masses.

BARITE- A native crystalline barium sulfate, which occurs in snow-white crystalline masses, or grayish, reddish, and greenish ores with a specific gravity of 4 to 4.6. It is used for increasing the density of oil well cement slurries and drilling fluids. See API Std 10A. Synonym - Barytes, heavy spar.

BARIUM SULFATE- BaSO4. See Barite.

BARREL- A volumetric unit of measure used in the petroleum industry consisting of 42 gal.

BARREL OF CEMENT- A dry weight measure of cement equal to 4 sacks or 376 pounds.

BARREL OF CEMENT SLURRY- 42 gallons of cement slurry.

BARREL EQUIVALENT- A laboratory unit used for evaluating or testing drilling fluids. One gram of material, when added to 350 ml of fluid, is equivalent to 1 lb of material when added to one 42-gal barrel of fluid.

BARREL WRENCH- A friction wrench used in repairing oil-well pumps.

BASE- A compound of metal, or a metal-like group, with hydrogen and oxygen in the proportion to form an OH radical, which ionizes in aqueous solution to yield excess hydroxyl ions. Bases are formed when metallic oxides react with water. Bases increase the pH. Examples are caustic soda and lime.

BARRIER ISLAND- A long, low, narrow wave-built island with elevations above high tide running parallel to a shoreline.

BASE EXCHANGE- The replacement of cations associated with the clay surface by those of another species, e.g., the conversion of sodium clay to calcium clay.

BASICITY- pH value above 7. Ability to neutralize or accept protons from acids.

BASTARD- Any equipment of non-standard shape or size.

BATCH- A definite amount of oil, mud, acid, or other liquid in a tank or pipe line.


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BEAM- The walking beam of a pumping jack or unit.

BEAM WELL- A well using a pumping jack or unit with rods to lift fluid.

BEAN- A choke, used to regulate flow of fluid from a well. Different sizes of beans are used for different producing rates.

BEAN BACK- To use a smaller-size bean or choke to make the amount of production smaller.

BED- A specific layer of earth or rock material in contrast to other layers of earth or rock of different material lying above, below, or adjacent to the bed in reference.

BELL HOLE- A bell-shaped hole dug beneath a pipe line to provide room- for use of tools.

BENCH MARKS- Permanent reference points of known elevation usually placed on concrete foundations, or on top of an iron stake driven securely into the ground.

BENTONITE- A highly plastic, highly colloidal clay, largely made up of the mineral, montmorillonite, plastic, colloidal clay, largely made up of the mineral sodium montmorillonite, a hydrated aluminum silicate. For use in drilling fluids, bentonite has a yield in excess of 85 bbl/ton. The generic term “bentonite” is neither an exact mineralogical name, nor is the clay of definite mineralogical composition.

BICARB- See Sodium Bicarbonate.

BIOCIDE- Used interchangeably with the word bactericide. “Bio” means life and “cide” means kill.

BIRD CAGE- To flatten and spread the strands in a wire rope.

BIRD DOG- To pay close attention to a job or a person, or an oil trader’s helper in securing an oil or gas lease.

BLANK FLANGE- (also a blind flange) A solid disc used to dead end a companion flange.

BLANK LINER- A liner without perforations.

BLANK-OFF- To close off, such as with a blank flange or bull plug.

BLOCKS, CROWN AND TRAVELING- The block and tackle on a rig that raises and lowers the drill string.

BLEED INTO- To cause a gas or liquid to mingle slowly with another gas or liquid, usually by pressure.

BLEED OFF OR BLEED DOWN- Reduce pressure by letting oil or gas escape at a low rate.

BLEEDER- A valve or pipe through which bleeding is done.

BLEEDING- Separation of the liquid phase in a cement slurry.


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BLOOIE LINE- Flow line for air or gas drilling.

BLOWDOWN- An operation by which accumulated sediment is blown from a boiler. Also applies to removal of surplus water from a boiler under pressure.

BLOWOUT- An uncontrolled escape of drilling fluid, gas, oil, or water from the well caused by the formation pressure being greater than the hydrostatic head of the fluid in the hole.

BLOWOUT PREVENTER- A device attached immediately above the casing, which can be closed and shut off the hole should a blowout occur.

BOB TAIL- Any short truck.

BOILERHOUSE- To make up or fake a report without actually doing the work.- To make up a report on a condition as fact without knowledge- of its accuracy. Sometimes referred to as “doghouse.”

BOLL WEEVIL- Any inexperienced worker or “hand.”

BOND- Adhering, binding, or joining of two materials; e.g., cement to casing.

BONDING- The state of bond between cement and casing and/or formation.

BONNET- The part of a valve that packs off and encloses the valve stem.

BOOMER- A link and lever mechanism which is used to tighten a chain holding a load on a truck.

BOREHOLE TELEVIEWER- A device for detecting fractures near the wellbore. This device sends a compressional wave and records the arrival time after the wave reflects off the borehole wall. A longer travel time indicates a fracture.

BOTTOM-HOLE PRESSURE- The pressure at the bottom of a well.

BOTTOMHOLE TREATING PRESSURE- The pressure in the wellbore at the perforations required to extend the fracture while overcoming closure pressure, fracture friction, and rock strength. See Fracture Extension Pressure.

BOTTOM WATER- Water occurring in a producing formation below the oil or gas in that same formation.

BOWL- A device into which fit the slips or wedges which support tubing.

BOWLINE- A knot much used in lifting heavy equipment with the catline. Its advantage lies in the fact that it can be readily untied irrespective of the load that has been placed on it.

BRACKISH WATER- Water containing low concentrations of any soluble salts.

BRADENHEAD GAS- Commonly called casinghead gas; gas that is produced with oil or from the casing head of an oil well.

BREAK CIRCULATION- To start movement of the drilling fluid after it has been quiescent in the hole.


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BREAKDOWN PRESSURE- The pressure observed from a well when the formation is fractured for the first time. This data is also useful in the drilling and cementing processes.

BREAKER- Chemicals that function by degrading the long chain polymer into shorter chains with controlled and predictable viscosity decrease.

BREAKOUT- Refers to the act of unscrewing one section of pipe from another section, especially in the case of drill pipe while it is being withdrawn from the well bore. During this operation the breakout tongs are used to start the unscrewing operation. Also refers to promotion of a crew member to the position of driller or of a driller to become a tool pusher. For example, “He broke out as driller at Conroe.”

BREAKOUT BLOCK- A heavy plate that fits in the rotary table and holds the drill bit while it is being unscrewed from the drill collar.

BREAKOUT, OIL- Oil that has risen to the surface of the mud, which previously had been combined in the mud as emulsion.

BREAKOUT TONG- See Breakout.

BREAK TOUR- Moving the rig and rigging-up is usually carried on during daylight hours only. When the rig is ready for operation on a new location, crews break tours and start operating 24 hours per day.

BREAKING DOWN- Usually means unscrewing the drill stem into single joints and placing them on the pipe rack. This operation takes place at the completion of the well when the drill pipe will no longer be used. It also takes place when changing from one size drill pipe to another during drilling operations. It is necessary to “break the pipe down” in order that it will be in lengths short enough to be handled and moved. Also called laying down.

BREAKTHROUGH RECOVERY- The oil recovery from a well or field prior to the instant when production of the displacing fluid occurs.

BRIDGING MATERIAL- Fibrous, flaky, or granular material added to a cement slurry or drilling fluid to aid in sealing formations in which lost circulation has occurred. See Lost Circulation Material.

BRINE- Water saturated with or containing a high concentration of common salt (sodium chloride); hence, any strong saline solution containing such other salts as calcium chloride, zinc chloride, calcium nitrate, etc.

BRINGING IN A WELL- The act of completing a well and bringing it into actual production status.

BROMINE VALUE- The number of centigrams of bromine that are absorbed by 1 g of oil under certain conditions. This is a test for the degree of unsaturatedness of a given oil.

BRONC- A term applied to a new driller recently promoted from helper. Also may apply to a new tool pusher recently promoted from driller.

BROWNIAN MOVEMENT- Continuous, irregular motion exhibited by particles suspended in a liquid or gaseous medium, usually as a colloidal dispersion.


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BS OR BS&W- Base sediment, or base sediment and water. Basic sediment, or basic sediment and water.

BUBBLE POINT- The pressure above which a hydrocarbon fluid exists only as a liquid; synonymous with saturation pressure.

BUCK UP- To tighten a threaded connection.

BUFFER- A substance or mixture capable in solution of neutralizing both acids and bases, thereby maintaining the original hydrogen-ion concentration.

BUG BLOWERS- A large fan installed on a drilling rig to blow insects away from the work area.

BUFFER- Any substance or combination of substances which, when dissolved in water, produces a solution which resists a change in its hydrogen ion concentration upon the addition of acid or base.

BUMP DOWN- To have too long a length of rods between the pumping jack and the pump seat so that the pump hits bottom on the downstroke.

BUMP OFF A WELL- To disconnect a pull-rod line from a central power unit. Same as “knock off a well.”

BURN PIT- An earthen pit in which waste oil and other materials are burned.

BY HEADS- A term applied to a flowing well when the flow is made intermittently.

BY-PASS- Usually refers to a pipe connection around a valve or other control mechanism. A by-pass is installed in such cases to permit passage of fluid through the line while adjustments or repairs are made on the control, which is by-passed.

CABLE-TOOL DRILLING- A method of drilling a well by allowing a weighted bit at the bottom of a cable to fall against the formation being penetrated. See Rotary Drilling.

CAGE- The part of a pump valve which holds the ball to limit its movement.

CAKE CONSISTENCY- According to API RP 13B, such notations as “hard,” “soft,” “tough,” “rubbery,” “firm,” etc., may be used to convey some idea of cake consistency.

CAKE THICKNESS- The measurement of the thickness of the filter cake deposited by a drilling fluid against a porous medium, most often following the standard API filtration test. Cake thickness is usually reported in 32nd of an inch. See Filter Cake and Wall Cake.

CALCIUM- One of the alkaline earth elements with a valence of 2 and an atomic weight of about 40. Calcium compounds are a common cause of the hardness of water. It is also a component of lime, gypsum, limestone, etc.

CALCIUM CARBONATE- CaCO3. An isoluble calcium salt sometimes used as a weighting material (limestone, oyster shell, etc.), in specialized drilling fluids. It is also used as a unit and/or standard to report hardness.


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CALCIUM CHLORIDE- CaC12. A very soluble calcium salt sometimes added to drilling fluids to impart special properties, but primarily to increase the density of the fluid phase.

CALCIUM CONTAMINATION Dissolved calcium ions in sufficient concentration to impart undesirable properties in a drilling fluid, such as flocculation, reduction in yield of bentonite, increase in fluid loss, etc. See also Calcium Sulfate, Gyp, Anhydrite, Lime, Calcium Carbonate.

CALCIUM HYDROXIDE- Ca(OH)2. The active ingredient of slaked lime. It is also the main constituent in cement (when wet). This material is referred to as “lime” in field terminology.

CALCIUM-TREATED MUDS- Calcium-treated muds are drilling fluids to which quantities of soluble calcium compounds have been added or allowed to remain from the formation drilled in order to impart special properties.

CALCIUM SULFATE- (Anhydrite: CaSO4; plaster of paris: CaSO4.1/2 H2O; and

gypsum: CaSO4.2H2O). Calcium sulfate occurs in muds as a contaminant or may be

added to certain muds to impart special properties.

CALIPER LOGGING- An operation to determine the diameter of the well bore or the internal diameter of casing, drill pipe, or tubing. In the case of the wellbore, caliper logging indicates undue enlargement of the bore due to caving condition or other causes. In the case of tubular goods, the caliper log reveals the internal corrosion.

CAPACITY- Ability of a reservoir to receive water.

CAPACITY INDEX- An indication of the capacity of a salt-water disposal well to take water. It is usually measured in barrels per hour per pound increase in bottom-hole pressure.

CAPILLARY PRESSURE- The retention or displacement force per unit area across a field interface resulting from the interaction of surface forces and the geometry of the medium in which they exist; the pressure difference across a fluid/fluid interface measurable under static conditions, natural energy mechanisms.

CASING CEMENTING- The practice of filling the annulus between casing and hole with cement in order to prevent fluid migration between permeable zones and to support the casing.

CASING PRESSURE- Gas pressure built up between the casing and tubing.

CAT- A crawler-type tractor noted for its ability to move over difficult terrain. It is much used in clearing the location, earth-moving operations, and skidding rigs. The operator or driver is frequently referred to as cat driver. This term is probably a shortening of the trade name Caterpillar, which is a brand of this type of equipment.

CAT DRIVER- See Cat.

CATALYST- A chemical useful for enhancing the rate at which a chemical reaction takes place while undergoing no chemical change itself.


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CATCHING SAMPLES- Geological information is obtained by studying samples of the formations penetrated by the drill. Members of the drilling crews obtain these samples from the drilling fluid as it emerges from the well bore. (Or from the bailer in case of cable tools.) This is known as catching samples. Cuttings so obtained should be carefully washed until free of foreign matter and then dried and accurately labeled to show the depth at which they were found.

CATION- The positively charged particle in the solution of anelectrolyte which, under the influence of an electrical potential, moves toward the cathode (negative electrode). Examples are: Na+, H+, NH4

+, Ca++, Mg++, Al+++.

CATIONIC- Refers to any cation (atom or chemical group bearing a positive electrical charge). It is used specifically to describe certain surfactants. A cationic surfactant ionizes to produce an anion (negatively charged ion) which is usually a non-metallic ion such as chloride or sulfate. When an anion is produced through ionization, a cation must also be produced. In this case, the cation is composed of the large organic portion of the molecule. The chloride or sulfate ion is always attached to the water soluble end of the surfactant molecule, so when the chloride or sulfate splits off in ionization, the water soluble end is left with a positive charge. Sand grains have a negative charge, so when a cationic surfactant is adsorbed on the sand grain surface, the positively charged (water soluble) end is attracted to the surface, leaving the oil soluble end sticking out. The sand grains are now said to be oil wet. Limestone and dolomite have a positive charge. When a cationic surfactant is adsorbed on these surfaces, the two positive charges repel each other and the oil soluble end of the cation is adsorbed on the surface, leaving the positively charged (water soluble) end sticking out. The limestone or dolomite is now said to be water wet. Most cationic surfactants will leave limestone or dolomite water wet, and sandstone oil wet.

CATLINE, CATHEAD, CATHEAD MAN, CATWALK- Catline - A line powered by the cathead, which is an extension of a shaft of the drawworks. Used to lift heavy equipment around the rig. Operated by the Cathead man. Cat walk - the ramp to the side of the drilling rig where pipe is laid out and lifted to the derrick floor by the catline.

CASING PRESSURE- Gas pressure built up between the casing and tubing.

CASINGHEAD GAS- Gas that is produced along with oil from an oil well.

CAUSTIC OR CAUSTIC SODA- See Sodium Hydroxide.

CAVE-IN- See Sloughing. Cave-in is a severe form of sloughing.

CAVERNOUS FORMATIONS- A formation having voluminous voids, usually the result of dissolving by formation waters which may or may not be still present.

CC OR CUBIC CENTIMETER- A metric-system unit for the measure of volume. It is essentially equal to the milliliter and commonly used interchangeably. One cubic centimeter of water at room temperature weighs approximately 1 g.

CELLAR- Excavation under the derrick to provide space for items of equipment at the top of the well bore. Also serves as a pit to collect drainage of water and other fluids under the floor for subsequent disposal by jetting.


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CEMENT- A mixture of calcium aluminates and silicates made by combining lime and clay while heating. Slaked cement contains about 62.5 percent calcium hydroxide, which is the major source of trouble when cement contaminates mud.

- (a) n.; A plastic material which hardens and forms a firm connection medium between two or more solids (b) v.t.; The- act of placing cement.

- Additive Cement - A cement or cement slurry to which an additive has been blended.

- ASTM Type Cement - A portland cement meeting the requirements of ASTM C150: Standard Specifications for Portland Cement.

- Common Cement - (a) API Class A cement; (b) ASTM Type I cement.

- Construction Cement - Normally, an ASTM Type I, II, or III portland cement (ASTM C 150: Standard Specifications for Portland Cement) and air-entraining modifications (ASTM C 175: Air Entraining Portland Cement). API Class A, B and C are similar to ASTM Type I, II and III, respectively. Air-entraining cements are not suitable for oil well cementing.

- Gel Cement - A cement or cement slurry that has been modified by the addition of bentonite.

- High Early Cement - (a) API Class C Cement; (b) ASTM Type III cement.

- High Temperature Cement - A cement composition designed to overcome strength retrogression.

- Hydraulic Cement - A cement that hardens or sets under water.

- Modified Cement - A cement whose properties, chemical or physical, have been altered by additives. This term has been used to refer to specific formulations of gel cement containing certain concentrations of dispersing agent.

- Neat Cement - A cement or cement slurry containing no additives.

- Oil-Well Cement - Cement or any mixture of cement with other materials that is intended for use in oil, gas, or water wells.

- Portland Cement - The product obtained by grinding clinker consisting essentially of hydraulic calcium silicates, to which no additions have been made subsequent to calcination other than water and untreated calcium sulfate, except that additions not to exceed 1.0% of other materials may be interground with the clinker at the option of the manufacturer, provided such materials in the amount indicated have been shown to be not harmful by tests carried out or reviewed by ASTM Committee C-1 on cement.

- Regular Cement - (a) API Class A cement, (b) ASTM Type I cement.

- Retarded Cement - A cement in which the thickening time is extended by adding a chemical retarder.


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- Slow-Set Cement - A cement in which the thickening time is extended by (1) eliminating the rapid hydrating components in its composition or (2) by adding a chemical retarder. API Class D, E, and F are slow-set cements.

- Sulfate-Resistant Cement - Cements which meet applicable requirements of API Std 10A.

- Weighted Cement - A cement slurry containing additives to increase its normal density.

CEMENT ADDITIVE- See Additive.

CEMENT DENSITY- The specific gravity of an oil well cement as determined by a method similar to ASTM C 188: Specific Gravity of Hydraulic Cement. Most portland cements have a specific gravity of about 3.15 when tested by this method. Cement density should not be confused with slurry density.

CEMENT SYSTEM- The combination of materials that make up an oil well cement slurry.

CEMENTING- The operation by which cement slurry is forced down through the casing and out at the lower end in such a way that it fills the space between the casing and the side of the well bore to a predetermined height above the bottom of the well. This is for the purpose of securing the casing in place and excluding water and other fluids from the well bore.

CEMENTING TIME- The total elapsed time for a cementing operation from the beginning of mixing until the completion of displacement to final depth and complete circulation of any excess slurry to the surface.

CENTIPOISE (CP)- A unit of viscosity equal to 0.01 poise. A poise equals 1 g per meter-second, and a centipoise is 1 g centimeter-second. The viscosity of water at 20°C is 1.005 cp (1 cp = 0.000672 lb/ft-sec).

CENTRALIZERS- Spring steel guides that are attached to casing to keep it centered in the hole.

CENTRIFUGE- A shake-out or grind-out machine. Samples of oil are placed in the machine and whirled at high speed to settle out sediment. A device for the mechanical separation of high specific gravity solids from a drilling fluid. Usually used on weighted muds to recover weight material and discard drill solids. The centrifuge uses high-speed mechanical rotation to achieve this separation, as distinguished from the cyclone-type separator in which the fluid energy alone provides the separating force. See Cyclone and Desander.

CHANGING RAMS- On rotary drilling rigs, blowouts are prevented by the device known as the blowout preventer. The sealing effect of the blowout preventer is accomplished by means of parts called rams. It is necessary to change the rams when drill pipe of a different size than that previously used is put in service.

CHASE THREADS- To straighten and clean threads of any kind.

CHEATER- A length of pipe used to increase the leverage of a wrench.


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CHELATE- From a Greek word meaning lobster’s claw, because there are two or more bonds holding a metallic ion to a molecule of the chelating substance. An action very similar to sequestration, but usually limited to the polycarboxylic acids. These materials are used in our work to prevent the precipitation of metallic ions such as calcium and iron, or to dissolve materials like gypsum.

CHEMICALS- In drilling-fluid terminology, a chemical is any material that produces changes in the viscosity, yield point, gel strength, and fluid loss, as well as surface tension.

CHEMICAL BARREL- A container in which various chemicals are mixed prior to addition to the drilling fluid.

CHERT- A quarzitic rock with hardness equal to or harder than flint.

CHISEL TONGS- Pipe tongs that grip the pipe with a chisel-like insert in the jaw of the wrench.

CHRISTMAS TREE- A term applied to the valves and fittings assembled at the top of a well to control the flow of the oil.

CHROMATE- A compound in which chromium has a valence of 6, e.g.,sodium bichromate. Chromate may be added to drilling fluids either directly or as a constituent of chrome lignites or chrome lignosulfonates. In certain areas, chromate is widely used as an anodic corrosion inhibitor, often in conjunction with lime.

CHROME LIGNITE- Mined lignite, usually leonardite, to which chromate has been added and/or reacted. The lignite can also be causticized with either sodium or potassium hydroxide.

CIRCULATE- To cycle drilling fluid through drill pipe and well bore while drilling operations are temporarily suspended. This is done to condition the drilling fluid and the well bore before hoisting the drill pipe and to obtain cuttings from the bottom of the well before drilling proceeds. Circulation of the drilling fluid while drilling is suspended is usually necessary to prevent drill pipe from becoming stuck.

CIRCULATION- The movement of drilling fluid from the suction pit through pump, drill pipe, bit, annular space in the hole, and back again to the suction pit. The time involved is usually referred to as circulation time.

CIRCULATION, LOST- The result of drilling fluid escaping into the formation by way of crevices or porous media.

CIRCULATION RATE- The volume flow rate of the circulating drilling fluid usually expressed in gallons or barrels per minute.

CLABBERED- A slang term commonly used to describe moderate to severe flocculation of mud due to various contaminants; also called “gelled-up.”

CLAY- A hydrated aluminum silicate. Clays are components of soils in varying percentages. Some types swell with absorption of water. Various types are: kaolinite, smectite, illite, chlorite and mixed-layer. A plastic, soft, variously colored earth, commonly a hydrous silicate of alumina, formed by the decomposition of feldspar and other aluminum silicates. See also Attapulgite, Bentonite, High Yield,


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Low Yield, and Natural Clays. Clay minerals are essentially insoluble in water but disperse under hydration, shearing forces such as grinding, velocity effects, etc., into the extremely small particles varying from submicron to 100-micron sizes.

CLAY CONTROL ADDITIVES- Chemical additives used to minimize the possibility of clay crystals breaking loose and migrating using ionic charge and organic polymer.

CLAY EXTENDER- Any of several substances, usually high molecular weight organic compounds that, when added in low concentrations to a bentonite or to certain other clay slurries, will increase the viscosity of the system, e.g., polyvinyl acetate-maleic anhydride copolymer. See Low-solids Muds.

CLIP- A U-bolt or similar device used to fasten parts of a wire cable together.

CLOSE NIPPLE- A very short piece of pipe having threads over its entire length.

CLOSED-IN- A well capable of producing oil or gas, but temporarily shut in.

CLOSED WATER-TREATING SYSTEM- A system of treating water in which the water does not coming in contact with air.

CLOSURE PRESSURE- There are two uses of this term: (1) The minimum hydraulic pressure required to hold a fracture open. This pressure is obtained from either minifracturing or microfracturing data. The closure pressure is the same Closure Pressure as the least principal rock stress. (2) This term is also used to refer to “closure stress,” or the stress the formation applies to the proppant bed after fracturing. Note: These two uses of this term should not be confused.

CLOSURE STRESS- The stress applied to the proppant bed after fracturing. Closure stress is not equal to closure pressure. Closure stress is equal to instantaneous shut-in pressure minus bottomhole flowing pressure. Consequently, closure stress in the proppant bed is a function of time.-

CLOSURE TIME- The time referenced from shut-in when the fracture closes. The analysis is based on SPE 8341 by K. G. Nolte.

CMC- See Sodium Carboxymethylcellulose.

COAGULATION- In drilling-fluid terminology, a synonym for flocculation. The joining together of finely divided particles of matter suspended in water, forming a mass large enough to settle out of suspension. A synonym for flocculation.

COALESCE- To combine into one body.

COALESCENCE- The change from a liquid to a thickened curdlike state by chemical reaction. Also the combination of globules in an emulsion caused by molecular attraction of the surfaces.

COHESION- The attractive force between the same kind of molecules, i.e., the force which holds the molecules of a substance together.

COKE- The solid carbon residue of a crude oil after all lighter components are removed by heat distillation.


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COLLAR- A pipe coupling threaded on the inside.

COLLOID- A state of subdivision of matter which consists either of single large molecules or of aggregations of smaller molecules dispersed to such a degree that the surface forces become an important factor in determining its properties. The size and electrical charge of the particles determine the different phenomena observed with colloids, e.g., Brownian movement. The sizes of colloids range from 1 x 10-7cm to 5 x 10-5cm (0.001 to 0.5 microns) in diameter, although the particle size of certain emulsoids can be in the micron range.

COLLOIDAL- Pertaining to suspended solids so finely divided that they will not settle.

COLLOIDAL COMPOSITION- A colloidal suspension containing one or more colloidal constituents.

COLLOIDAL SUSPENSION- Finely divided particles of ultra-microscopic size swimming in a liquid. A stable, homogeneous system of very fine particles of matter dispersed uniformly throughout a liquid medium, having properties which differ both from a true solution and from a suspension of larger particles. True colloidal suspensions have particle size range of 5 to 200 millimicron.

COMBINATION DRIVE RESERVOIR- An oil reservoir producing by two or more natural energy mechanisms.

COME-ALONG- A stretching or tightening device that crawls along a length of chain.

COMING OUT OF HOLE- Withdrawing of the drill pipe from the well bore. This withdrawal is necessary to change the bit, or change from bit to core barrel, to prepare for a drill stem test, and for other reasons.

COMPLEX- A compound formed by combination of two or more other compounds. A complex usually involves a metal and an organic compound. It is often reconvert- ible to the original simpler compounds.

COMPOUND- A chemical substance of fixed composition made up of two or more elements and having properties different from either of these.

COMPRESSIBILITY FACTOR- The ratio of the volume of a quantity of real gas at a pressure and temperature to the volume it would occupy were it an ideal or perfect gas; a factor used to correct a real gas for non-ideal behavior.

COMPRESSIVE STRENGTH- The degree of resistance of a material to force acting along one of the axes in a manner tending to crush it, usually expressed in pounds of force per square inch of surface affected. See API RP 10B.

CONDENSATE- Hydrocarbons which are in the gaseous state under reservoir conditions but which become liquid either in passage up the hole or at the surface.

CONDUCTIVITY- A measure of the quantity of electricity transferred across unit area per unit potential gradient per unit time. It is the reciprocal of resistivity. Electrolytes may be added to the drilling fluid to alter its conductivity for logging purposes.


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CONDUCTOR PIPE- A short string of casing of large diameter which is used in marshy locations and under certain other conditions. Its principal function is to keep the top of the well bore open and to provide means of conveying the upflowing drilling fluid from the well bore to the slush pit.

CONFORMING VOLUME- See volumetric conformance.

CONNATE WATER- (geologist) The water in the pore spaces of a rock which is all or part of the original water of deposition; (reservoir engineer) The irreducible minimum water content of a rock. Water inherent to the producing formation; or fossil sea water trapped in the pore spaces of sediments during their deposition.

CONNECTION- The joining of two lengths of pipe.

CONSISTENCY- The viscosity of a non-reversible fluid, in poises, for a certain time interval at a given pressure and temperature. A rheological property of matter which is related to the cohesion of the individual particles of a given material, its ability to deform, and its resistance to flow. The consistency of cement slurries is determined by thickening time tests in accordance with API RP 10B and is expressed in poise.

CONSISTOMETER- A thickening-time tester having a stirring apparatus to measure the relative thickening time for mud or cement slurries under predetermined temperatures and pressure. See API RP 10B*.

CONTAMINANTS- Materials, usually mud components, which become mixed with the cement slurry during the displacement process, and which have a deleterious effect on cement properties.

CONTAMINATION- The presence in a drilling fluid of any foreign material that may tend to produce detrimental properties of the drilling fluid.

CONTINUOUS PHASE- The fluid phase that completely surrounds the dispersed phase that may be colloids, oil, etc.

CONTRACT DEPTH- The depth of the well bore at which the drilling contract is fulfilled.

CONTROLLED AGGREGATION- A condition in which the clay platelets are maintained stacked by a polyvalent cation, such as calcium, and are deflocculated by use of a thinner.

CONVENTIONAL MUD- A drilling fluid containing essentially clay and water.

COPOLYMER- A substance formed when two or more substances polymerize at the same time to yield a product which is not a mixture of separate polymers but a complex having properties different from either polymer alone. See Polymer. Examples are polyvinyl acetate-maleic anhydride copolymer (clay extender and selective flocculant), acrylamide-carboxylic acid copolymer (total flocculant), etc.

CORING- The act of procuring a sample of the formation being drilled for geological information purposes. Coring is done by means of a core barrel. A conventional type of core barrel is put on the bottom of the drill pipe where the bit normally operates. As the cutter head of the core barrel penetrates the formations a


21 HRD Standards

continuous sample of the formation is taken in the core barrel and later withdrawn with the drill pipe. The wire line core barrel is used in many areas since it permits coring to be done without withdrawing the drill pipe from the well bore. Instead, a core barrel is dropped inside the drill pipe and automatically locks into coring position when it reaches the bottom of the well bore.

CORROSION- The adverse chemical alteration on a metal or the eating away of the metal by air, moisture, or chemicals; usually an oxide is formed. Deterioration of a metal due to a reaction with its environment.

CORROSION INHIBITOR INTENSIFIER- An additive that cannot be considered as an inhibitor when used alone but has the ability to improve the effectiveness of conventional organic inhibitors when used with them.

COUPON- Small metal strip which is exposed to corrosive systems for the purpose of determining nature and severity of corrosion.

C.P.- Point is cased hole of cementing through perforations. Also abbreviation for “casing point.”

CRACK A VALVE- To barely open a valve so that it leaks just a little.

CRATER (TO CRATER)- Term meaning the hole is caving in. To crater refers to the results that sometime accompany a violent blowout during which the surface surrounding the well bore falls into a large hole blown in the earth by the force of escaping gas, oil, and water. The crater sometimes covers an area of several acres and reaches a depth of several hundred feet. To crater also refers in oil field slang to any mishap which may occur to the men or the equipment.

CRATON- A relatively immobile large shield or platform.

CREAMING OF EMULSIONS- The settling or rising of the particles of the dispersed phase of an emulsion as observed by a difference in color shading of the layers formed. This can be either upward or downward creaming, depending upon the relative densities of the continuous and dispersed phases.

CREATED FRACTURES- Induced fractures by means of hydraulic or mechanical pressure exerted on the formation.

CRETACEOUS PERIOD- The latest period of the Mesozoic era. In the United States, cretaceous rocks are chiefly sedimentary, in part marine and in part terrestrial. They yield valuable quantities of coal, oil and gas.

CREVASSE- A crevice or parting in the surface of a glacier; a swampy overflow area associated with a delta-system stream channel.

CRINOLD- An echinoderm fossil, common as fragmental skeletal remains in Eocene and Oligocene formations.

CRITICAL POINT- The pressure and temperature where all lines of constant liquid content coverage for a given hydrocarbon mixture; the pressure and temperature at which all intensive properties of the vapor and liquid are the same.

CRITICAL PRESSURE- The point at which a constant pressure occurs indicating a reduction in the fracture extension rate (as defined by Nolte).


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CRITICAL SAND CONCENTRATION- The sand concentration at which the inlet fluid available for fluid leakoff is equal to the average fracture treatment leakoff rate.

CROSSLINKING- The union of high-polymer molecules by a system involving primary chemical bonds.

CROWBAR CONNECTION- A connection made with the parts in a bind or in a strain; a connection which requires force to be put together.

CROWN BLOCK- Sheaves and supporting beams on top of derrick.

CRUMB- To smooth out and even up the bottom of a ditch in which pipe is to be laid.

CURING- Aging of cement under specified conditions.

- Atmospheric Pressure Curing - The aging of cement specimens for test purposes at normal atmospheric pressure (14.7 psi at sea level), for a designated period of time under certain given conditions of temperature and humidity. See API RP 10B.

- Pressure Curing - The curing of cement specimens for test purposes, in water at pressure above atmospheric pressure. See API RP 10B.

CUT-OFF PERMEABILITY- A limiting permeability, usually too low to contribute to fluid flow or below which the rock contains only water or water and non-movable hydrocarbons.

CUT-OFF POROSITY- A limiting porosity; usually that below which the rock contains only water or non-movable hydrocarbons.

CUT OIL- Oil that contains water; also called wet oil.

CUTTINGS- Particles of formation obtained from a well during drilling operations. These are washed out while circulating mud-laden fluid in rotary drilling. They are bailed out in cable tool drilling.

CYCLE OF EROSION- The interval during which a land surface newly uplifted, either as plain or mountain, is worn down to the level of the sea.

CYCLE TIME, DRILLING FLUID- The time of a cycle, or down the hole and back, is the time required for the pump to move the drilling fluid in the hole. The cycle in minutes equals the barrels of mud in the hole divided by barrels per minute. *Recommended Practice for Testing Oil-well Cements and Cement Additives, American Petroleum Institute, Dallas, Texas, March (1965), 14th Ed.

CYCLONE- A device for the separation of various particles from a drilling fluid, most commonly used as a desander. The fluid is pumped tangentially into a cone, and the fluid rotation provides enough centrifugal force to separate particles by mass weight. See Centrifuge.

DARCY- A unit of permeability. A porous medium has a permeability of 1 darcy when a pressure of 1 atm on a sample 1 cm long and 1 sq cm in cross section will force a liquid of 1-cp viscosity through the sample at the rate of 1 cc per sec.


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DARCY’S LAW- The rate of flow of a homogeneous fluid through a porous medium is proportional to the pressure of hydraulic gradient and to the cross-sectional area normal to the direction of flow and inversely proportional to the viscosity of the fluid.

DAY WORK- When a drilling contract is entered into between an operator and a drilling contractor, it is frequently composed of two parts; namely, footage contract and day work. While the rig is on day work it is paid for on a daily basis at a price per day agreed upon. Day work arrangements usually cover drilling at extreme depths, coring, drill stem tests, and other operations where normal drilling operation are suspended for any reason at the request of the operator.

DEAD LINE- Refers to the end of the drilling line which is not reeled on the hoisting drum of the rotary rig. This end of the drilling line is usually anchored to the derrick substructure and does not move as the traveling block is hoisted, hence the term dead line.

DEAD MAN- A piece of wood or concrete, usually buried, to which a wire guy line is attached for bracing a mast or tower.

DEAD WELL- A well that will not flow.

DECONTAMINANTS- Materials added to cements or cement slurries for the specific purpose of counteracting the effects of contamination.

DEFLOCCULATION- Breakup of flocs of gel structures by use of a thinner.

DEFOAMER or DEFOAMER AGENT- Any substance used to reduce or eliminate foam by reducing the surface tension. Compare Antifoam.

DEGRADATION FACTOR- An indicator of the rheological degradation of the fracturing fluid. Its symbol is “a.” For harsh conditions (high temperature and/or high pressure), a = 2; for mild conditions, a = 0.

DEHYDRATION- Loss of water by filtration of cement slurries during or after displacement. Removal of free or combined water from a compound.

DELIQUESENCE- The liquefaction of a solid substance due to the solution of the solid by adsorption of moisture from the air, e.g., calcium chloride.

DELTA- The system of sediments and channels developed as a stream flows into a large body of standing water, such as a sea or lake.

DELTAIC DEPOSITS- Sedimentary deposits laid down in a river delta.

DENDRITIC- A branching figure resembling a shrub or tree produced on or in a fossil or rock. Stream drainage patterns of that configuration.

DENSITY- When used in relation to materials such as solids, liquids, or gases, this means the weight of a unit volume of the material. Many types of units are used to measure density. The chemist usually uses grams per cubic centimeter (gm/cc). In the oil patch we may use pounds per cubic foot (lb/cu ft) for solids, pounds per gallon (lb/gal) for liquids and pounds per cubic foot (lb/cu ft) for gases.


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- Matter measured as mass per unit volume expressed in pounds per gallon (lb/gal), pounds per square inch per 1,000 ft of depth (psi/1,000 ft), and pounds per cubic ft (lb/cu ft). Density is commonly referred to as “weight.”

- Mass per unit volume. Absolute density considers only the actual volume occupied by the material. Bulk density is mass per unit bulk volume that includes the actual volume of the material plus the volume of trapped air.

DEPLETION- A deduction allowed in computing the taxable income from oil and gas wells.

DEPLETION DRIVE RESERVOIR- An oil reservoir producing predominantly by the energy derived from pressure depletion and the resulting gas evolution and expansion internal to the oil zone; also referred to as solution gas drive.

DEPRECIATION- The decrease in value of any property such as a drilling rig due to normal wear or the passing of time. By including a charge for depreciation in cost of drilling, the drilling contractor accumulates funds to replace the drilling rig when it is worn out.

DERRICKMAN- The crew member whose work station is in the derrick while the drill pipe is being hoisted or lowered into the hole. He attaches the elevators to the stands of drill pipe while the pipe is being lowered into the hole and detaches the elevators while the pipe is being hoisted. Other responsibilities frequently include conditioning the drilling fluid and maintenance of the slush pumps. He is usually next in line of authority under the driller.

DESANDER- See Cyclone.

DESK AND DERRICK CLUBS- Organizations of women employed in the oil industry. Such clubs now exist in about a dozen major oil centers. The purpose of the organizations is partly educational and partly social.

DETRITAL- Referring to the fragmental or granular component of clastic rocks.

DEVONIAN PERIOD- The fourth period of the Paleozoic era, preceded by the Silurian and followed by the Carboniferous. Devonian rocks in the United States are chiefly marine sediments, though terrestrial beds are extensively developed in the Northeast. Considerable oil and gas are yielded by the Devonian Formations in the eastern United States.

DEW POINT- The pressure boundary of the two-phase region for a reservoir condensate fluid; the upper and lower pressure limits for which two phases can exist.

DIAGENESIS- The process leading to the lithification of a rock; the conversion of newly-deposited sediments into an indurated rock.

DIASTROPHISM- The process or processes by which the crust of the earth is deformed, producing continents and ocean basins, plateaus and mountains, flexures and folds of strata and faults. Also the results of these processes.

DIATOMACEOUS EARTH- An infusorial earth composed of siliceous skeletons of diatoms and being very porous. Sometimes used for combating lost circulation


25 HRD Standards

and as an additive to cement; also has been added to special drilling fluids for a particular purpose.

DIATOMACEOUS-EARTH FILTRATION- A process in which a filter cake or precoat of diatoms is used as a filter medium.

DIESEL-OIL PLUG- See Gunk Plug.

DIFFERENTIAL ETCHING- The removal of formation during fracturing acidizing in an uneven manner (hills and valleys). Once the formation closes, the area where the most rock was removed can act as permeable flow channels while the other areas act as support to keep these channels open.

DIFFERENTIAL PRESSURE- The difference in pressure between the hydrostatic head of the drilling-fluid column and the formation pressure at any given depth in the hole. It can be positive, zero, or negative with respect to the hydrostatic head.

DIFFERENTIAL-PRESSURE (WALL STICKING)- Sticking which occurs because part of the drill string (usually the drill collars) becomes embedded in the filter cake resulting in a non-uniform distribution of pressure around the circumference of the pipe. The conditions essential for sticking require a permeable formation and a pressure differential across a nearly impermeable filter cake and drill string.

DIFFUSION- The spreading, scattering, or mixing of a material (gas, liquid, or solid).

DILATANT FLUID- A dilatant or inverted plastic fluid is usually made up of a high concentration of well-dispersed solids which exhibits a non-linear consistency curve passing through the origin. The apparent viscosity increases instantaneously with increasing rate of shear. The yield point, as determined by conventional calculations from the direct-indicating viscometer readings, is negative; however, the true yield point is zero.

DILUENT- Liquid added to dilute or thin a solution.

DIRECT-INDICATING VISCOMETER- See Viscometer, Direct-indicating.

DIRECTIONAL DRILLING- While the normal well bore under usual conditions is planned to be drilled vertically, controlled directional drilling is sometimes used to drill a well at an angle from the vertical. Examples are the drilling of wells under the sea from a location on dry land and killing a blowout by means of a well drilled from a point at a safe distance from the one being brought under control. In the latter instance, the well bore drilled at an angle permits the pumping of heavy fluids into the bore of the well which is not under control. Modern development of this technique makes possible close control on both the direction and the degree of deviation of a directional well from the vertical.

DISPERSANT- Any chemical which promotes dispersion of the dispersed phase.

DISPERSANTS- A cement additive which reduces the consistency of cement slurries.


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DISPERSED PHASE- The scattered phase (solid, liquid, or gas) of a dispersion. The particles are finely divided and completely surrounded by the continuous phase.

DISPERSION (OF AGGREGATES)- Subdivision of aggregates. Dispersion increases the specific surface of the particle; hence results in an increase in viscosity and gel strength.

DISPERSOID- A colloid or finely divided substance.

DISPLACEMENT RATE- The volumetric flow rate at which cement slurry is pumped down the hole.

DISPOSAL WELL- A well through which water (usually salt water) is returned to subsurface formations.

DISSOCIATION- The splitting up of a compound or element into two or more simple molecules, atoms, or ions. Applied usually to the effect of the action of heat or solvents upon dissolved substances. The reaction is reversible and not as permanent as decomposition; i.e., when the solvent is removed, the ions recombine.

DISTILLATION- Process of first vaporizing a liquid and then condensing the vapor into a liquid (the distillate), leaving behind non-volatile substances, the total solids of a drilling fluid. The distillate is the water and/or oil content of a fluid.

DOG-LEG- The “elbow” caused by a sharp change of direction in the well bore. A bend in pipe, a ditch, or a well.

DOGHOUSE- A small house used for keeping lease records, changing clothes, or any other use around a lease.

DONKEY PUMP- Any little pump; used for many kinds of small temporary pumping operations.

DOODLEBUG- A slang term for the seismograph that is used in prospecting for potential oil-bearing geological structures. Also is applied to various devices used in searching for petroleum deposits.

DOPE- Material used on threads of pipe or tubing to lubricate and prevent leakage.

DOUBLE- Two lengths or joints of pipe joined together.

DOUGHNUT- A ring of wedges that supports a string of pipe or a threaded, tapered ring used for the same purpose.

DOWNCOMER- A pipe through which flow is downward.

DOZER- A powered machine for earthwork excavations.

DRESSER SLEEVE- A slip-type collar that is used to join plain-end pipe.

DRESSING- Sharpening (as in the case of a drag bit), repairing, and replacing parts to make items of equipment ready for re-use. The term applies especially to drilling bits and tool joints.

DRIFTER- A worker who never stays long in one place.


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DRILL-STEM TEST (DST)- A test to determine whether oil and/or gas in commercial quantities has been encountered in the well bore.

DRILL STRING- The string of pipe that extends from the bit to the Kelly, carries the mud down to the bit, and rotates the bit.

DRILLER- The employee directly in charge of a drilling ring and crew. Operation of the drilling and hoisting equipment constitute his main duties.

DRILLING BLOCK- Usually a lease or a number of leases of adjoining tracts of land which constitute a unit of acreage sufficient to justify the expense of drilling a wildcat well.

DRILLING FLUIDS- Any fluid, such as air or gas, water- or oil-base muds, circulated in a well during drilling operations.

DRILLING IN- The operation during the drilling procedure at the point of drilling into the pay formation.

DRILLING MUD OR FLUID- A circulating fluid used in rotary drilling to perform any or all of various functions required in the drilling operation.

DRILLING OUT- The operation during the drilling procedure when the cement is drilled out of the casing before further hole is made or completing attempted.

DRILLING UNDER PRESSURE- Carrying on drilling operation while maintain a seal at the top of the well bore to prevent the well fluids from blowing out.

DRIP- Equipment designed to remove small quantities of liquids from a gas stream.

DRY BASIS- The weight of an additive corrected for moisture.

DRY BLENDING- The process of admixing finely-divided solid components.

DRY COMBUSTION- In-situ combustion with the injection of dry air only.

DRY GAS- A hydrocarbon fluid which exists at a reservoir temperature above its cricondentherm; a gas which cannot be liquified by pressure change alone. Natural gas that is produced with liquids; also a gas that has been treated to remove all liquids.

DRY HOLE- Somewhat loosely used in oil work, but in general any well that does not produce oil or gas in commercial quantities. A dry hole may flow water, or gas, or may even yield some oil to the pump, but no in commercial quantities.

DUSTER- A non-productive well. A dry hole.

DUTCHMAN- The portion of a stud or screw which remains in place after the head has been twisted off in an effort to remove the entire stud or screw. Also used to refer to a tool joint pin broken off in the drill-pipe box or drill-collar box.

DYNAMIC- The state of being active or in motion; opposed to static.

EFFECTIVE PERMEABILITY- The permeability to one fluid in a multi-fluid system.


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EFFECTIVE POROSITY- The ratio of the interconnected void space volume to the bulk volume of the rock.

EFFECTIVE SIZE- A term used in specifying sand. It is the sieve size in millimeters that permits 10 percent of the filter sand by weight to pass.

ELECTRIC LOGGING- A term used in specifying sand. it is the sieve size in millimeters that permits 10 percent of the filter sand by weight to pass. Electric logs are run on a wire line to obtain information concerning the porosity, permeability, fluid content of the formations drilled, and other information. The drilling-fluid characteristics may need to be altered to obtain good logs.

ELECTROLYTE- A substance which dissociates into charged positive and negative ions when in solution or a fused state and which will then conduct an electric current. Acids, bases, and salts are common electrolytes.

ELEMENT- The basic building blocks of all materials or compounds. An element cannot be further decomposed by chemical means. Examples are: iron, sulfur, oxygen, hydrogen. We often use the word elemental to precede the name of an element to signify that it is not combined with another element, such as “elemental sulfur.”

ELEVATION- Height above sea level.

ELEVATORS- Latches which secure the drill pipe; attached to the traveling block which raises and lowers the pipe from the hole.

EMULISIFER OR EMULSIFYING AGENT- A substance used to produce an emulsion of two liquids that do not mix. Emulsifiers may be divided, according to their behavior, into ionic and non-ionic agents. The ionic types may be further divided into anionic, cationic, and amphoteric, depending upon the nature of the ion-active groups. A surface active agent capable of stabilizing an emulsion.

EMULSION- A substantially permanent heterogeneous liquid mixture of two or more liquids that do not normally dissolve in each other but which are held in suspension or dispersion, one in the other, by mechanical agitation or, more frequently, by adding small amounts of substances known as emulsifiers. Emulsions may be mechanical, chemical, or a combination of the two. They may be oil-in-water or water-in-oil types. An intimate mixture of liquids mutually insoluble, one of which is distributed throughout the other in the form of globules. A mixture of two or more liquids which do not normally dissolve in each other but which are held in suspension, one in the other. The suspension is usually stabilized by small amounts of additional substances known as emulsifiers. These modify the surface tension of the droplets to keep them from gathering together and forming two separate liquid layers. A mixture of two or more liquids which do not normally dissolve in each other but are held in suspension, one in the other. The suspension is usually stabilized by small amounts of additional substances known as emulsifiers. These modify the surface tension of the droplets to keep them from gathering together and forming two separate liquid layers. We usually deal with emulsions of crude oil or diesel with an aqueous fluid such as acid or water. Emulsions may be classified as oil-external or water-external. In an oil-external emulsion, the aqueous phase exists as tiny globules which are coated with a thin


29 HRD Standards

layer of the hydrocarbon phase. Most emulsion breakers are designed to work on this type emulsion. They do not work as well on water-external emulsions.

EMULSOID- Colloidal particles which take up water.

END POINT- Indicates the end of some operation or when a definite change is observed. In titration this change is frequently a change in color of an indicator which has been added to the solution or the disappearance of a colored reactant.

ENGINEER, MUD OR DRILLING-FLUID- One versed in drilling fluids whose duties are to manage, carry through, and maintain the various types of oil-well mud programs.

ENHANCED RECOVERY- Any oil recovery beyond that obtainable by conventional waterflooding.

ENZYME- One of a group of complex organic substances formed in the living cells of plants and animals. They are necessary catalysts for the chemical reactions of biological processes (such as digestion).

EP ADDITIVE- See Extreme-pressure Lubricant.

EPM OR EQUIVALENTS PER MILLION- Unit chemical weight of solute per million unit weights of solution. The epm of a solute in solution is equal to the ppm (parts per million) divided by the equivalent weight. Refer also to Ppm.

EQUILIBRIUM CONSTANT (RATIO)- The ratio of the moles of vapor and liquid of a single, pure substance or component at a temperature and pressure.

EQUIVALENT CIRCULATING DENSITY- For a circulating fluid, the equivalent circulating density in lb/gal equals the hydrostatic head (psi) plus the total annular pressure drop (psi) divided by the depth (ft) and by 0.052.

EQUIVALENT WEIGHT OR COMBINING WEIGHT- The atomic or formula weight of an element, compound, or ion divided by its valence. Elements entering into combination always do so in quantities proportional to their equivalent weights.

EXPANDED PERLITE- A siliceous volcanic rock that is ground to small size and subjected to extreme temperature in an oven, resulting in an expansion and release of combined water, leaving the rock particle considerably expanded and porous.

EXPANSION LOOP- A bend placed in a line to absorb stretch or shrinkage.

EXTRAPOLATED THICKENING TIME- The time required for a cement slurry to reach a consistency of 100 Vc obtained by extending the curve recorded during a thickening time test which may be stopped at 70 Vc under given conditions. See API RP 10B.

EXTREME-PRESSURE LUBRICANT- Additives which, when added to the drilling fluid, impart lubrication to the bearing surfaces when subjected to extreme pressure conditions.

EYEBALL- To straighten or align pipe by eye.


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FALSE SET- An abnormal early thickening of cement slurry wherein the slurry remains pumpable for the usual thickening time. The thickening may be reversible during the pumping history of the slurry.

FAST LINE- The end of the drilling line that is affixed to the drum or reel. It is so called because it apparently travels with greater velocity than any other portion of the drilling line.

FATIGUE- Failure of a metal under repeated loading.

FAULT- Geological term denoting a formation break, upward or downward, in the subsurface strata. Faults can significantly affect the area mud and casing programs.

FEED-OFF- The act of unwinding a cable from a drum. A device on a drilling rig that keeps the weight on the bit constant and lowers the drilling line automatically. Known as the “automatic driller.”

FEMALE CONNECTION- A pipe or rod coupling with the threads on the inside.

FERMENTATION- Decomposition process of certain organic substances, e.g., starch in which a chemical change is brought about by enzymes, bacteria, or other micro-organisms. Often referred to as “souring.”

FIBER OR FIBROUS MATERIALS- Any tough string material used to prevent loss of circulation or to restore circulation. In field use, fiber generally refers to the larger fibers of plant origin.

FIELD- The area around a group of producing oil wells.

FILLER MATERIAL- A material added to a cement or cement slurry for the primary purpose of increasing the yield of the slurry.

FILLING THE HOLE- Pumping drilling fluid continuously or intermittently into the well bore to maintain the fluid level in the hole near the surface. The purpose is to avoid danger of blowout, water intrusion, and/or caving of the well bore, e.g., as the pipe is withdrawn.

FILLUP LINE- The line through which fluid is added to the hole.

FILTER- A porous medium through which fluid is passed to separate it from material held in suspension.

FILTER CAKE- The suspended solids that are deposited on a porous medium during the process of filtration. See also Cake Thickness.

FILTER-CAKE TEXTURE- The physical properties of a cake as measured by toughness, slickness, and brittleness. See also Cake Consistency.

FILTER-CAKE THICKNESS- A measurement of the solids deposited on filter paper in 32nd of an inch during the standard 30-min API filter test. See Cake Thickness. In certain areas the filter-cake thickness is a measurement of the solids deposited on filter paper for a 7½-min duration.

FILTER LOSS- A misnomer sometimes applied to fluid loss.


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FILTER PAPER- Porous unsized paper for filtering liquids. API filtration test specifies on thickness of 9-cm filter paper Whatman No. 50, S&S No. 576, or equivalent.

FILTER PRESS- A device for determining fluid loss of a drilling fluid having specifications in accordance with API RP 13B.

FILTRATE- The liquid that is forced through a porous medium during the filtration process. For test, see Fluid Loss.

FILTRATION- The process of separating suspended solids from their liquid by forcing the latter through a porous medium. Two types of fluid filtration occur in a well: dynamic filtration while circulating, and static filtration when at rest.

FILTRATION QUALITIES- The filtration characteristics of a drilling mud. Generally these qualities are inverse to the thickness of the filter cake deposited on the face of a porous medium and the amount of filtrate allowed to escape from the drilling fluid into or through the medium.

FILTRATION RATE- See Fluid Loss.

FINAL SET- Cement shall be considered to have acquired its final set when it will bear, without appreciable indentation, the final Gillmore needle. This is not an API test. See ASTM C 266: Time of Setting of Hydraulic Cement by Gillmore Needles.

FINAL STRENGTH- The strength of a cement at such a time when under the given conditions of temperature and pressure it ceases to change significantly. Synonym - Ultimate Strength.

FINENESS- The particle size to which a cement clinker is ground. This value is generally reported as surface area as determined with the Blaine air permeability apparatus or Wagner turbidimeter.

FINGER BOARD- A rack located in the derrick to support stands of pipe while stacked in the derrick.

FISH- An object accidentally lost in the hole.

FISHING- Operations on the rig for the purpose of retrieving from the well bore sections of pipe, collars, junk, or other obstructive items that are in the hole.

FISSURES- The natural cracks or fractures that occur in a formation.

FIRE WALL- A wall of earth built around an oil tank to hold the oil if the tank breaks or burns.

FIREMAN- The member of the crew on a steam-powered rig who is responsible for the care and operation of the boilers. On a mechanical rig his counterpart is the motorman.

FITTINGS- The small pipes and valves that are used to make up a system of piping.


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FLAG- To tie a piece of cloth or other marker on a bailing or swabbing line to enable the operator to know the depth at which the swab or bailer is operating in the hole.

FLANGE UP- The act of making the final connection on the piping system. Also in oil field slang it refers to the completion of any operation. Frequently refers to quitting a job.

FLARE- An open flame used to dispose of unwanted gas around a completed well.

FLASH POINT- The lowest temperature at which a combustible liquid will give off a flammable vapor which can be ignited and will burn momentarily.

FLASH SET- Flash set is abnormal early thickening or setting of cement slurry wherein the cement slurry becomes unpumpable.

FLAT GEL- A condition wherein the 10-min gel strength is substantially equal to the initial gel strength.

FLIPPED- When the opposite occurs of what is intended in a drilling fluid. In an invert water-in-oil emulsion, the emulsion is said to be flipped when the continuous and dispersed phases reverse.

FLOAT- A long flat-bed semi-trailer.

FLOCCULATES- Groups of aggregates or particles in suspension subject to being broken up by normal shaking and stirring and reforming on standing.

FLOCCULATING AGENT- Substances, such as most electrolytes, some polysaccharides, certain natural or synthetic polymers, that bring abut the thickening of the consistency of a drilling fluid. In Bingham plastic fluids, the yield point and gel strength increase.

FLOCCULATION- Loose association of particles in lightly bonded groups, non-parallel association of clay platelets. In concentrated suspensions, such as drilling fluids, flocculation results in gelation. In some drilling fluids, flocculation may be followed by irreversible precipitation of colloids and certain other substances from the fluid, e.g., red beds.

FLOCS- See Flocculates.

FLOODING- The process of drowning out a well with water; also the process by which oil is sometimes driven from the sand into the well by water introduced under pressure into a key well.

FLOORMAN- A member of the drilling crew whose work station is about the derrick floor. On rotary drilling rigs normally there are two floormen on each drilling crew.

FLOW A WELL HARD- To let a well flow at too high a rate.

FLOW BEAN- A plug in the flow line at the well head which has a small hole drilled through it through which oil flows, and which keeps a well from flowing at too high a rate.


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FLOW BY HEADS- A well flowing oil at irregular intervals.

FLOW CHART- A chart made by a recording meter, which shows rate of production.

FLOWING WELL- A well that produces oil or gas without any means of artificial lift.

FLOW LINES- The surface pipes through which oil travels from the well to storage.

FLOW TANK- A lease storage tank to which produced oil is run.

FLOW TREATER- A single unit that acts as an oil and gas separator, an oil heater, and an oil and water treater.

FLUID- A fluid is a substance readily assuming the shape of the container in which it is placed. The term includes both liquids and gases. It is a substance in which the application of every system of stresses (other than hydrostatic pressure) will produce a continuously increasing deformation without any relation between time rate of deformation at any instant and the magnitude of stresses at that instant. Drilling fluids are usually Newtonian and plastic, seldom pseudoplastic, and rarely dilatant fluids.

FLUID EFFICIENCY- The ratio of the volume of fluid injected minus the volume leaked off during injection to the total volume of fluid pumped in.

FLUID FLOW- The state of fluid dynamics of a fluid in motion is determined by the type of fluid (e.g., Newtonian, plastic, pseudoplastic, dilatant), the properties of the fluid such as viscosity and density, the geometry of the system, and the velocity. Thus, under a given set of conditions and fluid properties, the fluid flow can be described as plug flow, laminar (called also Newtonian, streamline, parallel, or viscous) flow, or turbulent flow. See terms and Reynolds number.

FLUID INJECTION- The injection of an extraneous fluid into an oil or gas reservoir as a means of improving recovery.

FLUID LEVEL- Distance between well head and point to which fluid rises in the well.

FLUID LOSS- The volume of fluid lost to a permeable material due to the process of filtration. The API fluid loss is the volume of fluid in a filtrate as determined according to the Fluid-Loss Test given in API RP 10B. See Water Loss.

FLUID-LOSS ADDITIVE- An additive used to reduce the fluid loss of cement slurries. Material used to maintain adequate injected fluid within the created fracture and to minimize damage by controlling fluid leak-off.

FLUID MOBILITY- The instantaneous ratio of the effective permeability for a fluid to its viscosity.

FLUID PHASE- A definable physical state of fluid; e.g., oil, gas, water, liquid, vapor, etc.


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FLUIDITY- The reciprocal of viscosity. The measure of rate with which a fluid is continuously deformed by a shearing stress. Ease of flowing.

FLUORESCENCE- Instantaneous re-emission of light of a greater wavelength than that light originally absorbed.

FLUSH PRODUCTION- The high rate of flow made by a good well right after it is drilled.

FOAM- A foam is a two-phase system, similar to an emulsion, where the dispersed phase is a gas or air. A dispersion of a gas in a liquid.

FOAMING AGENT- A substance that produces fairly stable bubbles at the air-liquid interface due to agitation, aeration, or ebullition. In air or gas drilling, forming agents are added to run water influx into aerated foam. This is commonly called “mist drilling.” A surface active agent capable of stabilizing a foam.

FORMATION DAMAGE- Damage to the productivity of a well resulting from invasion into the formation by mud particles or mud filtrates. Asphalt from crude oil will also damage some formations. See Mudding Off.

FORMATION PRESSURE- Pressure at the bottom of a well that is shut in.

FORMATION SENSITIVITY- The tendency of certain producing formations to adversely react with invading mud filtrates.

FORMATION VOLUME FACTOR- The reservoir pore volume occupied by a unit volume of stock-tank oil and its associated gas.

FOURBLE- A section of drill pipe, casing or tubing consisting of four joints screwed together. See Double; Thribble.

FOURBLE BOARD- A platform installed in the derrick at an elevation of 80 feet to 120 feet above the derrick floor. The derrickman works on this board while the pipe is being hoisted from or lowered into the well bore.

FRACTURE- Cracks and crevices in the formation either inherent or induced.

FRACTURE COMPLIANCE- The ratio of the average width to the net pressure in the fracture (as defined by Nolte).

FRACTURE ENTRY FRICTION- The combination of perforation friction and flow tortuosity in the immediate vicinity of the wellbore.

FRACTURE EXTENSION PRESSURE- The lowest pressure at which a fracture will propagate. Fracture extension pressure is the “bottomhole treating pressure” measured at the perforations. It is required in calculating horsepower requirements and in the design of computer models.

FRACTURE OPENING PRESSURE- The pressure required to open an existing fracture. Because this pressure is sometimes close to the closure pressure, these terms are often used synonymously. Since the fracture extension pressure is obtained after the opening pressure, these terms are sometimes used interchangeably.


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FRACTURING- Application of hydraulic pressure to the reservoir formation to create fractures through which oil or gas may move to the well bore.

FRONTAL DISPLACEMENT- The displacement of oil or gas by means of an advancing body of a different fluid.

FRONTAL ZONE- The zone of displacement for an advancing injected fluid.

FROST UP- Icing of equipment due to the cooling effect of expanding gas.

FROZEN UP- Said of equipment of which the components do not operate freely.

FUNCTIONS OF DRILLING FLUIDS- The most important function of drilling fluids in rotary drilling is to bring cuttings from the bottom of the hole to the surface. Some other important functions are: control subsurface pressures, cool and lubricate the bit and drill string, deposition of an impermeable wall cake, etc.

FUNICULAR WATER (SATURATION)- Water held on the surfaces of rock pores solely by wetting forces.

FUNNEL VISCOSITY- See Marsh Funnel Viscosity.

G FUNCTION- The dimensionless pressure difference function described in SPE 8341.

GAGING NIPPLE- A small section of pipe in the top of a tank through which a tank may be gaged.

GALENA- Lead sulfide (PbS). Technical grades (specific gravity about 7) are used for increasing the density of drilling fluids to points impractical or impossible with barite.

GAS CUT- Gas entrained by a drilling fluid or cement. See Air Cutting.

GAS-CAP DRIVE RESERVOIR- An oil reservoir producing predominantly by the energy derived from expansion of an associated gas cap; also referred to as segregation drive.

GAS CONDENSATE- A hydrocarbon fluid which exists at a reservoir temperature above that of the critical point and below cricondentherm of the mixture.

GAS DEVIATION FACTOR- See compressibility factor.

GAS IN SOLUTION- The quantity of gas that is evolved from reservoir oil as it is removed to stock-tank pressure and temperature.

GAS-OIL RATIO- The number of cubic feet of gas produced with a barrel of oil.

GAS VOLUME FACTOR- The ratio of the volumes occupied by a mass quantity of gas at two conditions of pressure and temperature, usually reservoir and standard conditions.

GATHERING LINES- The flow lines which run from several wells to a single tank battery.


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GEL- A state of a colloidal suspension in which shearing stresses below a certain finite value fail to produce permanent deformation. The minimum shearing stress that will produce permanent deformation is known as the shear or gel strength of the gel. Gels commonly occur when the dispersed colloidal particles have a great affinity for the dispersing medium, i.e., are lyophilic. Thus gels commonly occur with bentonite in water. For their measurement, see Gel Strength, Initial and 10 min. A term used to designate highly colloidal, high-yielding, viscosity-building commercial clays, such as bentonite and attapulgite clays. (a) Usually refers to sodium bentonite clays belonging to the general class of montmorillonites. (b) The colloidal suspension in such a state that shearing stresses below a certain finite value fail to produce permanent deformation. A viscous solution or semi-solid dispersion of a solid in a liquid. The solids may be either natural polymers or synthetic polymers. These solids are composed of fibrous strings of extremely long molecules. The polymer particles swell when placed in a fluid and take part of the fluid into the fibrous structure. This gives the fluid viscosity which may vary from a slight thickening of the fluid to the creation of a rigid gel similar to set gelatin. Gels are clear or translucent.

GEL CEMENT- Cement having a small to moderate percentage of bentonite added as a filler and/or to reduce the slurry weight. See Gunk Plug.

GEL STRENGTH- The value of the shear stress required to cause permanent deformation of a colloidal suspension. The ability or the measure of the ability of a colloid to form gels. Gel strength is a pressure unit usually reported in lb/100 sq ft. It is a measure of the same interparticle forces of a fluid as determined by the yield point except that gel strength is measured under static conditions, yield point under dynamic conditions. The common gel-strength measurements are initial and the 10-min gels (which see). See also Shear and Thixotropy.

GEL STRENGTH, INITIAL- The measured initial gel strength of a fluid is the maximum reading (deflection) taken from a direct-reading viscometer after the fluid has been quiescent for 10 sec. It is reported in lb/100 sq ft. See API RP 13B for details of test procedure.

GEL STRENGTH, 10 MIN- The measured 10-min gel strength of a fluid is the maximum reading (deflection) taken from a direct-reading viscometer after the fluid has been quiescent for 10 min. The reading is reported in lb/100 sq ft. See API RP 13B for details of test procedure.

GELLED UP- Oil-field jargon usually referring to any fluid with high gel strength and/or highly viscous properties. Often a state of severe flocculation.

GELATION- Association of particles to form a continuous structure.

GILSONITE- A naturally occurring solid hydrocarbon belonging to the asphalt group. A granular form of gilsonite is sometimes used as a cement additive.

GIN-POLE TRUCK- A truck equipped with a pair of poles, and hoisting equipment for use in lifting heavy machinery around a lease.

GIRTH OR GIRT- One of the horizontal braces between the legs of a derrick.

GONE TO WATER- Describes a well in which water production is increasing.


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GPG OR GRAINS PER GALLON- Ppm (which see) equals gpg x 17.1.

GRASS GOOSER- A hoe or other kind of weed cutter.

GRAVITY DRAINAGE RESERVOIR- An oil reservoir producing predominantly by gravitational forces and fluid density.

GRAVITY GATHERING SYSTEM- A gathering system that depends upon the natural fall of ground level for the movement of fluid.

GRAVITY PRESSURE HEAD- The head of pressure created by the weight of water, rather than pressure as a result of pumping.

GRAVITY, SPECIFIC- The weight of a particular volume of any substance compared to the weight of an equal volume of water at a reference temperature. For gases, air is usually taken as the reference substance, although hydrogen is sometimes used.

GREASING OUT- Certain organic substances, usually fatty-acid derivatives, which are added to drilling fluids as emulsifiers, e.p. lubricants, etc., may react with such ions as calcium and magnesium that are in or will subsequently come into the system. An essentially water-insoluble greasy material separates out.

GRIND OUT- See Shake Out.

GROSS FRACTURE HEIGHT- The total fracture height.

GROSS INTERVAL- The vertical distant between persistent and correlatable log markers above and below the entire reservoir interval.

GROSS RESERVOIR INTERVAL- The vertical distance between the top and base of the total reservoir rock.

GROSS SAND- The total thickness of reservoir-type rock within the gross reservoir interval.

GROUTING- The filling of void space with a substance that hardens (grout). It is performed to prevent passage of fluids or gases or to prevent compaction of materials in a formation.

GUAR GUM- A naturally occurring hydrophilic polysaccharide derived from the seed of guar plant. The gum is chemically classified as a galactomannan. Guar gum slurries made up in clear fresh or brine water possess pseudoplastic flow properties.

GUM- Any hydrophilic plant polysacchrides or their derivatives which, when dispersed in water, swell to produce a viscous dispersion or solution. Unlike resins, they are soluble in water and insoluble in alcohol.

GUMBO- Any relatively sticky formation, such as clay, encountered in drilling.

GUNK PLUG- A slurry in crude or diesel oil containing any of the following materials or combinations; bentonite, cement, attapulgite, and guar gum (never with cement). Used primarily in combatting lost circulation. The plug may or may not be squeezed.


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GUNK SQUEEZE- A bentonite, diesel-oil mixture that is pumped down the drill pipe to mix with drilling mud being pumped down the annulus. These two mix to form a stiff, putty-like material that can be squeezed into lost circulation zones.

GUNNING THE PITS- Mechanical agitation of the drilling fluid in a pit by means of a mud gun, electric mixer, or agitator.

GUY WIRE- A rope or cable used to steady a mast or pole.

GYP OR GYPSUM- See Calcium Sulfate. Gypsum is often encountered while drilling. It may occur as thin stringers or massive formations.

HANDY- A connection that can be unscrewed by hand.

HANG A WELL OFF- To stop operation of jack operating from a central power unit by disconnecting the rod line.

HARDNESS (OF WATER)- The hardness of water is due principally to the calcium and magnesium ions present in the water and is independent of the accompanying acid ions. The total hardness is measured in terms of parts per million of calcium carbonate or calcium and sometimes equivalents per million of calcium. For hardness tests, see API RP 13B.

HATCH- An opening into a tank, usually through the top deck.

HAY TANK- A tank or enclosure filled with hay-like material used to filter oil out of water.

HEADACHE- A warning cry given when anything is dropped from overhead.

HEADACHE POST- A frame built over a truck cab to prevent pipe from falling on the cab.

HEAT (A CONNECTION)- To loosen a collar or other threaded connection by striking it with a hammer.

HEAT BALANCE- The summation of heat generated, lost, and remaining at a point in space over a period of time.

HEAVING- The partial or complete collapse of the walls of a hole resulting from internal pressures due primarily to swelling from hydration or formation gas pressures. See Sloughing.

HETEROGENEOUS- A substance that consists of more than one phase and is not uniform, such as colloids, emulsions, etc. It has different properties in different parts. The prefix “hetero” means unlike. When you say a formation is heterogeneous, it means that it has parts that are unlike other parts. These parts may differ in density, permeability, porosity, mineral composition, etc.

HIGH-pH MUD- A drilling fluid with a pH range above 10.5. A high-alkalinity mud.

HIGH-YIELD DRILLING CLAY- A classification given to a group of commercial drilling-clay preparations having a yield of 35 to 50 bbl/ton and intermediate between bentonite and low-yield clays. High-yield drilling clays are usually


39 HRD Standards

prepared by peptizing low-yield calcium montmorillonite clays or, in a few cases, by blending some bentonite with the peptized low-yield clay.

HOLD-DOWN- A clamp used on rod line posts to keep the rod from moving in any direction but back and forth.

HOMOGENEOUS- Of uniform or similar nature throughout; or a substance or fluid that has at all points the same property or composition. The prefix “homo” means same or like. When you describe a formation as being homogeneous, you mean that it is essentially the same throughout the zone.

HOPPER, JET- See Mud-mixing Devices. A device to hold or feed drilling-mud additives.

HORIZONTAL EFFECTIVE STRESS- See Least Principal Stress.

HOT OIL- Oil produced in violation of state regulations or transported interstate in violation of federal regulations.

HUFF AND PUFF- Cyclic steam injection; thermal recovery by steam injection whereby injection and production cycles are alternated in each well.

HUMIC ACID- Organic acids of indefinite composition in naturally occurring leonardite lignite. The humic acids are the most valuable constituent. See Lignin.

HYDRAFRAC- A copyrighted name of an operation whereby producing formations are fractured by hydraulic pressure to increase productiveness.

HYDRATE- A substance containing water combined in the molecular form (such as CaSO4

o2H²O). A crystalline substance containing water of crystallization.

HYDRATION- The act of a substance to take up water by means of absorption and/or adsorption.

HYDRAULIC GRADIENT- The quotient of the change in pressure head between any two points along a line of flow and the actual length of stream between the points.

HYDROCARBON- A compound consisting only of molecules of hydrogen and carbon.

HYDROGEN ION CONCENTRATION- A measure of the acidity or alkalinity of a solution, normally expressed as pH. See pH.

HYDROLYSIS- Hydrolysis is the reaction of a salt with water to form an acid and base. For example, soda ash (Na2CO3) hydrolyzes basically, and hydrolysis is responsible for the increase in the pH of water when soda ash is added.

HYDROMETER- A floating instrument for determining the specific gravity or density of liquids, solutions, and slurries. A common example is the Mudwate hydrometer used to determine the density of mud.

HYDROPHILE- A substance usually in the colloidal state or an emulsion, which is wetted by water; i.e., it attracts water or water adheres to it.


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HYDROPHILIC- A property of a substance having an affinity for water or one that is wetted by water.

HYDROPHILIC-LIPOPHILIC BALANCE (HLB)- The hydrophilic-lipophilic balance (HLB) is one of the most important properties of emulsifiers. It is an expression of the relative attraction of an emulsifier for water and oil, determined largely by the chemical composition and ionization characteristics of a given emulsifier. The HLB of an emulsifier is not directly related to solubility, but it determines the type of an emulsion that tends to be formed. It is an indication of the behavior characteristics and not an indication of emulsifier efficiency.

HYDROPHOBE- A substance, usually in the colloidal state, not wetted by water.

HYDROPHOBIC- Descriptive of a substance which repels water.

HYDROSTATIC HEAD- The pressure exerted by a column of fluid, usually expressed in pounds per square inch. To determine the hydrostatic head at a given depth in psi, multiply the depth in feet by the density in pounds per gallon by 0.052.

HYDROXIDE- A designation that is given for basic compounds containing OH- radical. When these substances are dissolved in water, they increase the pH of the solution. See Base.

HYGROSCOPIC- The property of a substance enabling it to absorb water from the air.

IDIOT SPOON OR STICK- Any shovel, rake, hoe, or other similar hand tool.

IDLER- In machinery an idler pulley or sprocket is used in connection with belt drive and chain drive respectively to maintain desired tension on the belt or chain. Such a pulley or sprocket has no other purpose.

IGNORANT END- The heaviest end of a piece of equipment.

ILMENITE- An iron-black mineral of composition FeOoTiO2 having a specific gravity of 4.67. It is used for increasing the density of oil-well cement slurries and drilling fluids.

IMPRESSION PACKER- A packer made from uncured rubber sections. After pressuring the rubber and returning the packer to the surface, the azimuth of the fracture (±20o) may be determined.

IMPROVED RECOVERY- Oil recovery beyond that obtainable by primary means alone.

INDICATOR- Substances in acid-base titrations which, in solution, change color or become colorless as the hydrogen ion concentration reaches a definite value, these values varying with the indicator. In other titrations such as chloride, hardness, and other determinations, these substances change color at the end of the reaction. Common indicators are phenolphthalein, potassium chromate, etc

INHIBITED MUD- A drilling fluid having an aqueous phase with a chemical composition that tends to retard and even prevent (inhibit) appreciable hydration (swelling) or dispersion of formation clays and shales through chemical and/or physical means. See Inhibitor (Mud).


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INHIBITOR- A substance that minimizes the amount of corrosion on metal in contact with a corrosive medium. For stimulation purposes, an inhibitor is most often used to limit acid corrosion of tubular and pumping equipment.

INHIBITOR (CORROSION)- Any agent which, when added to a system, slows down or prevents a chemical reaction or corrosion. Corrosion inhibitors are used widely in drilling and producing operations to prevent corrosion of metal equipment exposed to hydrogen sulfide, carbon dioxide, oxygen, salt water, etc. Common inhibitors added to drilling fluids are filming amines, chromates, and lime.

INHIBITOR (MUD)- Substances generally regarded as drilling mud-contaminants, such as salt and calcium sulfate, are called inhibitors when purposely added to mud so that the filtrate from the drilling fluid will prevent are retard the hydration of formation clays and shales.

INITIAL GEL- See Gel Strength, Initial.

INITIAL SET- Cement shall be considered to have acquired its initial set when it will bear, without appreciable indentation, the initial Gillmore needle. This is not an API test. See ASTM C 266: Time of Setting of Hydraulic Cement by Gillmore Needles.

INORGANIC- Compounds of earthy or mineral origin such as: water, limestone, dolomite, gypsum, HCl, etc; no carbon compounds are included except cyanides or carbonates.

IN-SITU COMBUSTION- A Thermal recovery method whereby heat is generated within the reservoir by burning heavier components of the oil. The setting afire of some portion of the reservoir in order that the gases produced by combustion will drive oil ahead of it to the producing wells.

INSPECTION SPOOL- A short length of pipe inserted in a pipeline in such a manner that it is easily removed for inspection. It should be of the same material as the remainder of the pipeline.

INSTANTANEOUS SHUT-IN PRESSURE- The pressure observed during a hydraulic fracturing operation immediately following the shut-in of the well which negates pressure transients. The difference between the fracture extension pressure and the instantaneous shut-in pressure is the frictional pressure drop across the perforations to the fracture tip. This term is abbreviated as ISIP or Pisi.

INSULATING FLANGE- A flange that incorporates plastic pieces to separate the metal parts.

INTERFACIAL TENSION- The tensile strength, due to molecular forces, of the surface of a fluid in the presence of a dissimilar fluid. The force required to break the surface between two immiscible liquids. The lower the interfacial tension between the two phases of an emulsion, the greater the ease of emulsification. When the values approach zero, emulsion formation is spontaneous. See Surface Tension. The forces existing in the interface, or boundary layer, between two unlike liquids. This tension results from unbalanced intermolecular forces in the boundary region. It can actually be measured by a very sensitive instrument called a


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tensiometer. The force required to pull a small ring through the interface is used as measure of interfacial tension and is expressed as dynes/cm. Interfacial tension is a factor in the formation or breaking of emulsions and in the recovery of treating fluids from matrix permeability.

INTERSTITIAL WATER- Any and all water within the interstices or voids of formations.

INVERT OIL-EMULSION MUD- A water in oil emulsion where fresh or salt water is the- dispersed phase and diesel, crude or some other oil is the continuous phase. Water increases the viscosity and oil reduces the viscosity.

IODINE NUMBER- The number indicating the amount of iodine absorbed by oils, fats, and waxes, giving a measure of the unsaturated linkages present. Generally, the higher the iodine number, the more severe the action of the oil on rubber.

ION- Acids, bases, and salts (electrolytes) when dissolved in certain solvents, especially water, are more or less dissociated into electrically charged ions or parts of the molecules, due to loss or gain of one or more electrons. Loss of electrons results in positive charges producing a cation. A gain of electrons results in the formation of an anion with negative charges. The valence of an ion is equal to the number of charges borne by it.

IONIZATION- This is sometimes called dissociation and refers to the separation of molecules in solution into positively and negatively charged particles. These charged particles are called ions. Ionization is considered to be a reversible reaction, and the greater the concentration of molecules, the less the percent that will exist as ions. Hydrochloric acid is a solution of hydrogen chloride gas in water. It is represented by the chemical shorthand formula of HCL. When HCL ionizes in solution, it forms a hydrogen ion and a chloride ion, as noted by this equation:

HCL - H+ + Cl-

- Note that the hydrogen ion has a positive charge and the chloride ion has a negative charge. Positively charged ions are called cations. Negatively charged ions are called anions.

- Refers to the separation of molecules in solution into positively and negatively charged particles. These charged particles are called ions. Ionization is considered to be a reversible reaction, and the greater the concentration of molecules, the less the percent that will exist as ions. Hydrochloric acid is a solution of hydrogen chloride gas in water. It is represented by the chemical shorthand formula of HC1.

IRREDUCIBLE WATER SATURATION- The water saturation within a rock held by wetting and capillary forces, the residual water saturation after flushing with an immiscible fluid, a saturation which cannot be further reduced by dynamic forces without changes to the chemistry and/or temperature of the system.

JACK BOARD- A device used to support the end of a length of pipe while another length is being screwed on.

JACK LINES- The pull-rod lines running from a central power unit to a pumping jack.


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JET-PERFORATING- An operation similar to gun-perforating except that a shaped charge of high explosives is used to burn a hole through the casing instead of the gun which fires a projectile in gun-perforating. This use of explosives originated during World War II as a defensive measure against tanks.

JETTING- A process of periodically removing a portion of, or all of, the water, mud and/or solids, from the pits usually by means of pumping through a jet nozzle arrangement.

JOINT- A length of pipe - usually from 20 to 30 ft. long.

JONES EFFECT- The net surface tension of salt solutions first decreases with an increase of concentration, passes through a minimum, and then increases as the concentration is raised.

KELLY OR KELLY JOINT- A heavy square pipe or other configuration that works through a like hole in the rotary table and rotates the drill stem.

KEY SEAT- That section of a hole, usually of abnormal deviation and relatively soft formation, which has been eroded or worn by drill pipe to a size smaller than the tool joints or collars. This keyhole type configuration will not allow these members to pass when pulling out of the hole.

KILL A WELL- To overcome pressure in a well by use of mud or water so that surface connections may be removed.

KILL LINE- A line connected to the annulus below the blowout preventers for the purpose of pumping into the annulus while the preventers are closed.

KILLING A WELL- Bringing a well under control that is blowing out. Also the procedure of circulating water and mud into a completed well before starting well service operations.

KINEMATIC VISCOSITY- The kinematic viscosity of a fluid is the ratio of the viscosity (e.g., cp in g/cm-sec) to the density (e.g., g/cc) using consistent units. In several common commercial viscometers the kinematic viscosity is measured in terms of the time of efflux (in seconds) of a fixed volume of liquid through a standard capillary tube or orifice. See Marsh Funnel Viscosity.

KNOCK-OFF BLOCK OR POST- The post and hook that are used to hang off a well operated through a rod line.

KNOCKOUT- A kind of tank or filter used to separate oil and water.

KNUCKLE BUSTER- A wrench that is liable to slip.

LAB BURN- The simulation of the in-situ combustion process in a laboratory sand-packed, oil-saturated tube.

LACT- “Lease Automatic Custody Transfer,” possible where measuring equipment installed at the point of transfer from lease to pipeline is so completely automated as not to require any manual activity or witnesses.

LAMINAR FLOW- Fluid elements flowing along fixed streamlines which are parallel to the walls of the channel of flow. In laminar flow, the fluid moves in


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plates or sections with a differential velocity across the front, which varies from zero at the wall to a maximum toward the center of flow. Laminar flow is the first stage of flow in a Newtonian fluid; it is the second stage in a Bingham plastic fluid. This type of motion is also called parallel, streamline, or viscous flow. See Plug and Turbulent Flow. Fluid flow where neighboring layers are not mixed.

LATEX- Colloidal suspension or emulsion of organic materials. Certain latexes are sometimes used as cement additives.

LAZY BOARD- See Jack Board.

LEAK-OFF- Loss of fluid from a hydraulically created fracture to the matrix of the formation.

LEASE POWER- A central unit that provides the power to pump more than one well.

LEAST PRINCIPAL STRESS- The smallest principal stress in an elemental cube with one face oriented normal to the vertical. This stress is also referred to as Horizontal Effective Stress, Horizontal Stress, Closure Pressure or HST.

LEONARDITE- A naturally occurring oxidized lignite. See Lignins.

LIGNINS, MINED OF HUMIC ACIDS- Mined lignins are naturally occurring special lignite, e.g., leonardite, that are produced by strip mining from special lignite deposits. The active ingredient is the humic acids. Mined lignins are used primarily as thinners, which may or not be chemically modified. However, they are also widely used as emulsifiers.

LIGNOSULFONATES- Organic drilling-fluid additives derived from by-products of sulfite paper manufacturing process from coniferous woods. Some of the common salts, such as the ferrochrome, chrome, calcium, and sodium, are used as universal dispersants while others are used selectively for calcium-treated systems. In large quantities, the ferrochrome and chrome salts are used for fluid-loss control and shale inhibition.

LIME- Commercial form of calcium hydroxide.

LIME-TREATED MUDS- Commonly referred to as “lime-base” muds. These high-pH systems contain most of the conventional fresh-water additives to which slaked lime has been added to impart special properties. The alkalinities and lime contents vary from low to high.

LIMESTONE- See Calcium Carbonate.

LINER- Any string of casing whose top is situated at any point below the surface.

LIPOPHILE- A substance usually colloidal and easily wetted by oil.

LIPOPHILIC- Having an affinity for oil.

LIVE OIL- Crude oil that contains gas and has not been stabilized or weathered. This oil can cause gas cutting when added to mud and is a potential fire hazard.


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LOAD BINDER- Chain or rope used to tie down loads of equipment, or the “boomer” used to tighten the chains.

LOCATION- The place at which a well is to be or has been drilled.

LOG- A running account listing a series of events in chronological order. The driller’s log is a tour-to-tour account of progress made in drilling. Electric well log is a record of geological formations which is made by a well logging device. This device operates on the principle of differential resistance of various formations to the transmission of electric current.

LOGGING- See Mud Logging and Electric Logging.

LOSS OF CIRCULATION- See Circulation, Loss of.

LOSS OF HEAD OR FRICTION LOSS- See Pressure-drop Loss.

LOST CIRCULATION- The result of drilling fluid escaping into the formation by way of crevices or porous media.

LOST-CIRCULATION ADDITIVES- Materials added to the mud to control or prevent lost circulation. These materials are added in varying amounts and are classified as fiber, flake, or granular.

LOST CIRCULATION MATERIAL- A material added to cement slurries or drilling fluids, which is designed to prevent the loss of cement or mud to the formation. See Bridging Material.

LOST RETURNS- See Lost Circulation.

LOW-SOLIDS MUDS- A designation given to any type of mud where high performingadditives, e.g., CMC, have been partially or wholly substituted for commercial or natural clays. For comparable viscosity and densities (weighted with barite), a low-solids mud will have a lower volume-percent solids content.

LOW-YIELD CLAYS- Commercial clays chiefly of the calcium montmorillonite type having a yield of approximately 15 to 30 bbl/ton.

LYOPHILIC- Having an affinity for the suspending medium, such as bentonite in water.

LYOPHILIC COLLOID- A colloid that is not easily precipitated from a solution and is readily dispersible after precipitation by an addition of the solvent.

LYOPHOBIC COLLOID- A colloid that is readily precipitated from a solution and cannot be redispersed by an addition of the solution.

MAKE A HAND- To become a good worker.

MAKE IT UP ANOTHER WRINKLE- To make up a connection one more turn.

MALE CONNECTION- A connection with the threads on the outside.

MANHOLE- A hole in the side of a tank through which a man can enter the tank, also the clean-out plate.


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MARGINAL WELL- An oil or gas well the production of which is so limited in relation to production costs that profit approaches the vanishing point.

MARSH FUNNEL- An instrument used in determining the Marsh funnel viscosity. The Marsh funnel is a container with a fixed orifice at the bottom so that when filled with 1,500 cc fresh water, 1 qt (946 ml) will flow out in 26 ± 0.5 sec. For 1,000 cc out, the efflux time for water is 27.5 ± 0.5 sec. See API RP 13B for specifications.

MARSH FUNNEL VISCOSITY- Commonly called the funnel viscosity. The Marsh funnel viscosity is reported as the number of seconds required for a given fluid to flow 1 qt through the Marsh funnel. In some areas, the efflux quantity is 1,000 cc. See API RP 13B for instructions. See also Kinematic Viscosity.

MASTER GATE- A large valve used to shut in a well.

MATCH PRESSURE- Denoted by P*, or Pm. It is defined as the pressure from a pressure difference vs. a dimensionless pressure difference graph, which corresponds to a curve from a dimensionless pressure vs. dimensionless time master plot. The curve matching yields P* which is used to calculate a fluid loss coefficient. Note: Care should be take not to confuse the P* match pressure with the P* used with Horner analysis of well testing.

MATERIAL BALANCE- In reservoir engineering, a volumetric balance which states that since the volume of a reservoir is constant, the algebraic sum of the volume changes of the oil, free gas, and water volumes must be zero.

MATRIX FLOW- The flow of fluids through the permeable formation.

MECHANICAL RIG- A drilling rig whose source of power is one or more internal-combustion engines.

MENSICUS- The curved upper surface of a liquid column, concave when the containing walls are wetted by the liquid and convex when not.

MESH- A measure of fineness of a woven material, screen, or sieve; e.g., a 200-mesh sieve has 200 openings per linear inch. A 200-mesh screen with a wire diameter of 0.0021 in. (0.0533 mm) has an opening of 0.074 mm, or will pass a particle of 74 microns. See Micron.

Mf- The methyl orange alkalinity of the filtrate, reported as the number of milliliters of 0.02 Normal (N/50) acid required per milliliter of filtrate to reach the methyl orange end point (pH 4.3).

MICA- A naturally occurring flake material of varying size used in combatting lost circulation. Chemically, an alkali aluminum silicate.

MICELLES- Organic and inorganic molecular aggregates occurring in colloidal solutions. Long chains of individual structural units chemically joined to one another and laid side by side to form bundles. When bentonite hydrates, certain sodium or other metallic ions go into the solution, the clay particle plus its atmosphere of ions is technically known as a micelle.


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MICROFRACTURE- A small penny shaped fracture created with a small amount of fluid (on the order of l0s of gallons) at a low injection rate (for example, 2 to 20 gallons per minute). The purpose of this test is to obtain the least principal rock stress in the formation of interest and, sometimes, to indicate the orientation of the fracture.

MICRONu = Mu- A unit of length equal to one millionth part of a meter, or one thousandth part of a millimeter.

MILK EMULSION- See Oil-emulsion Water.

MILLIDARCY- 1/1000 darcy. See Darcy.

MINI-FRACTURING- A series of tests performed to obtain important information pertinent to the design of the main fracturing job. These tests include a step rate test, a pump-in, flow-back test and a pressure decline test. These tests yield the fracture extension pressure, the closure pressure, the instantaneous shut-in pressure, the opening pressure, the closure time, and the fluid loss coefficient. Further analysis yields the fracture width and the fracture length.

MINIMUM WATER- The minimum water content of a cement slurry determined by the procedure given in Section 3 of API RP 10B.

MISCIBLE- The solubility of one liquid in another. When a solid dissolves in a liquid, we say it is soluble in the liquid, as salt is soluble in water. When speaking of liquids, we say that they are immiscible, partially miscible, totally miscible, or miscible in all proportions.

MISCIBILITY PRESSURE- The pressure at which two otherwise dissimilar fluids are mixable in all proportions to form a continuous single-phase liquid.

MISCIBLE DISPLACEMENT- The displacement of oil or gas by a separate fluid with no interface existing at the displacement front.

MISCIBLE FLOOD- An oil-recovery process which involves the injection of a solvent followed by a displacing fluid.

MISCIBLE SLUG DISPLACEMENT- The displacement of oil by a volume of lighter hydrocarbon liquid (usually) with which it is miscible.

MIST DRILLING- A method of rotary drilling whereby water and/or oil is dispersed in air and/or gas as the drilling fluid.

Ml OR MILLILITER- A metric system unit for the measure of volume. Literally 1/1000 of a liter. In drilling-mud analysis work, this term is used interchangeably with cubic centimeter (cc). One quart is about equal to 946 ml.

MOBILITY RATIO- The ratio of two fluid mobilities, usually the displacing and displaced fluids.

MOLECULAR WEIGHT- The sum of the atomic weights of all the constituent atoms in the molecule of an element or compound.

MOLECULE- When atoms combine they form a molecule. In the case of an element or a compound, a molecule is the smallest unit that chemically still retains


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the properties of the substance in mass. The smallest particle of a compound that still retains the properties of the compound.

MONOMER- The simple molecules that join together to form a polymer are known as monomers and their union is called polymerization. k-TROLtm is pumped into a well as a monomer and polymerizes in the formation to form a polymer.

MONTMORILLONITE- A clay mineral commonly used as an additive to drilling muds. Sodium montmorillonite is the main constituent in bentonite. The structure of montmorillonite is characterized by a form that consists of a thin platey-type sheet with the width and breadth indefinite, and thickness that of the molecule. The unit thickness of the molecule consists of three layers. Attached to the surface are ions that are replaceable. Calcium montmorillonite is the main constituent in low-yield clays.

MOVABLE OIL IN PLACE- The reservoir oil volume or saturation which will flow under forces of pressure depletion or fluid displacement.

MUD- A water- or oil-base drilling fluid whose properties have been altered by solids, commercial and/or native, dissolved and/or suspended. Used for circulating out cuttings and many other functions while drilling a well. Mud is the term most commonly given to drilling fluids (which see).

MUD ADDITIVE- Any material added to a drilling fluid to achieve a particular purpose.

MUDDING OFF- Commonly thought of as reduced productivity caused by the penetrating, sealing, or plastering effect of a drilling fluid.

MUDDING UP- Process of mixing mud additives to achieve some desired purpose not possible with the former fluid, which usually has been water, air, or gas.

MUD HOUSE- A structure at the rig to store and shelter sacked materials used in drilling fluids.

MUD LOGGING- A method of determining the presence or absence of oil or gas in the various formations penetrated by the drill bit. The drilling fluid and the cuttings are continuously tested on their return to the surface, and the results of these tests are correlated with the depth or origin.

MUD-MIXING DEVICES- The most common device for adding solids to the mud is by means of the jet hopper. Some other devices for mixing are: educators, paddle mixers, electric stirrers, mud guns, chemical barrels, etc.

MUD PIT- Earthen or steel storage facilities for the surface mud system. Mud pits which vary in volume and number are of two types: circulating and reserve. Mud testing and conditioning is normally done in the circulating pit system.

MUD PROGRAM- A proposed or followed plan or procedure for the type(s) and properties of drilling fluid(s) used in drilling a well with respect to depth. Some factors that influence the mud program are the casing program and such formation characteristics as type, competence, solubility, temperature, pressure, etc.

MUD PUMPS- Pumps at the rig used to circulate drilling fluids.


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MUD SCALES- See Balance, Mud.

MUD STILL- An instrument used to distill oil, water, and other volatile material in a mud to determine oil, water, and total solids contents in volume-percent.

MULE HEAD- A horse head, the curved device on the oil-well end of a walking beam.

MULTIPLE COMPLETION- A well completion which provides for simultaneous production from separate zones.

NATURAL CLAYS- Natural clays, as opposed to commercial clays, are clays that are encountered when drilling various formations. The yield of these clays varies greatly, and they may or may not be purposely incorporated into the mud system.

NATURAL POLYMER- A polymer product obtained from a natural source, generally a plant source. See Polymer.

NEAT CEMENT- A slurry composed of portland cement and water.

NET FRACTURE HEIGHT- The fracture height in the pay zone or through a zone where fluid loss occurs. Net fracture height is also referred to as fluid loss height.

NET PAY- The net sand thickness actually containing oil and/or gas.

NET PRESSURE- The bottomhole treating pressure minus closure pressure. The net pressure acts to propagate a fracture.

NET SAND- The thickness of all porous and permeable reservoir type rock within the gross sand interval.

NEUTRALIZATION- A reaction in which the hydrogen ion of an acid and the hydroxyl ion of a base unite to form water, the other ionic product being a salt.

NEWTONIAN FLOW- See Newtonian Fluid.

NEWTONIAN FLUID- Fluids with the same apparent viscosity irregardless of the pump rate or agitation, for example, water , oil, molasses.

NON-CONDUCTIVE MUD- An drilling fluid, usually oil-base or invert-emulsion muds, whose continuous phase does not conduct electricity, e.g., oil. The spontaneous potential (SP) and normal resistivity cannot be logged, although such other logs as the induction, acoustic velocity, etc., can be run.

NON-EMULSIFIER- A substance which demulsifies (breaks) emulsions or prevents their formation.

NON-FOAMING AGENT- A substance that destabilizes or breaks a foam.

NONIONIC- Refers to surfactants which do not ionize and to molecules which neither have positive nor negative charges. They have oil-soluble and water- soluble ends and the wettability characteristics are related to the relative sizes of these ends. Many nonionics will water wet both limestone and sand. They are often blended with anionics or cationics.


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NON-MOVABLE OIL IN PLACE- The reservoir oil volume or saturation that will not flow under forces of pressure depletion or fluid displacement.

NON-NEWTONIAN FLUIDS- Fluids that the apparent viscosity changes with agitation or pump rate, for example, gels, emulsions, polymers, mayonnaise. These are fluids which experience apparent viscosity changes with agitation or pump rate. Examples are gels, emulsions or polymers.

NORMAL CRUDE OIL- A reservoir oil for which all physical properties can be defined satisfactorily by pressure and temperature only.

NORMAL SOLUTION- A solution of such a concentration that it contains 1 gram-equivalent of a substance per liter of solution.

OFF PRODUCTION- Said of a well when it is shut in or temporarily not able to produce.

OFFSET WELL- Well drilled near another one.

OIL-BASED MUD- The term “oil-based mud” is applied to a special type drilling fluid where oil is the continuous phase and water the dispersed phase. Oil-based mud contains blown asphalt and usually 1 to 5 percent water emulsified into the system with caustic soda or quick lime and an organic acid. Silicate, salt, and phosphate may also be present. Oil-based muds are differentiated from invert-emulsion muds (both water-in-oil emulsions) by the amounts of water used, method of controlling viscosity and thixotropic properties, well-building materials, and fluid loss.

OIL CONTENT- The oil content of any drilling fluid is the amount of oil in volume-percent.

OIL AND WATER SEPARATION FACILITY- The gun barrel, settling tank, water knockout, or emulsion treater, installed by the lease owner for the purpose of separating produced oil and water.

OIL-COUNTRY TUBULAR GOODS- Oil-well casing, tubing, or drill pipe.

OIL-EMULSION WATER (MILK EMULSION)- A drilling fluid in which the oil content is usually kept between 3 to 7 percent and seldom over 10 percent (it can be considerably higher). The oil is emulsified into fresh or salt water with a chemical emulsifier. Sometimes CMC, starch, or gum may be added to the fresh- and salt-water systems.

OIL FIELDS- An area where oil is found. A loosely-defined term referring to an area in which one or more separate pools or reservoirs may be found.

OIL STRING- A string of casing used to keep the oil well open through the rock formations, down to or through the producing formation.

OIL-IN-WATER EMULSION MUD- Commonly called “emulsion mud.” Any conventional or special water-base mud to which oil has been added. The oil becomes the dispersed phase and may be emulsified into the mud either mechanically or chemically.

OLD HAND- A man who has been around the oil field for a long time.


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ON THE LINE- Said of a tank when it is being emptied into a pipe line.

ON THE PUMP- Said of a well that is being pumped.

OPEN HOLE- The uncased part of the well.

OPEN WATER-TREATING SYSTEM- A system of treating water in which the water comes in contact with air.

OPERATOR- The person, whether proprietor or lessee, actually operating a mine or oil well or lease.

OPERATING PRESSURE- The pressure at which a line or system is operating at any given time.

OPTIMUM WATER- The amount of water used in a cement slurry that gives the slurry the best properties for its particular application.

ORGANIC- Compounds of carbon or carbon and hydrogen (hydrocarbons). Other elements may be present in the make-up of the compound. Examples are: acetic acid, formic acid, all alcohols, natural gas, propane, and crude oil.

OVERPRODUCED- Said of a well that has produced more than is allowable.

OXIDATION- Originally meant the combination of oxygen with some substance. Now any chemical change in which the valence or oxidation state of an element is increased is referred to as oxidation. Oxidation is always accompanied by reduction; that is, when the valence of one element is increased, the valence of another is decreased. An example of oxidation involving a combination with oxygen is that when natural gas and butane burn, they combine with oxygen from the air to form carbon dioxide and water. An example of oxidation, meaning a valence change is that the recovery of elemental sulfur from hydrogen sulfide in natural gas. In this case, the sulfur in the H2S is oxidized from a valence of 2- to a valence of 0 in the elemental sulfur state. Another example is the corrosion of steel by acid. In this case, the iron in the steel is oxidized from a valence of 0 to 2+, while the hydrogen from the acid is reduced from a valence of 1+ to 0. This results in the iron dissolving while the hydrogen is released as a gas.

OXIDIZING AGENT- Any material which causes oxygen to be combined with another element or causes the valence of another element to be increased. Thus, oxygen itself is an oxidizing agent in the combustion of fuel. Examples of compounds which are oxidizing agents are sodium persulfate, sodium dichromate, potassium permanganate, and hydrogen peroxide.

PACKER FLUID- Any fluid placed in the annulus between the tubing and casing above a packer. Along with other functions, the hydrostatic pressure of the packer fluid is utilized to reduce the pressure differentials between the formation and the inside of the casing and across the packer itself.

PARTICLE- A minute unit of matter, usually a single crystal, or of regular shape with a specific gravity approximating that of a single crystal.

PARTS PER MILLION- See Ppm.

PARALLEL FLOW- See Laminar Flow.


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PAY ZONE OR PAY FORMATION- The formation drilled into that contains oil and/or gas in commercial quantities.

PENDULAR WATER (SATURATION)- Water held in the smaller pore crevices of a rock primarily by capillary forces.

PENETRATION, RATE OF- The rate in feet per hour at which the drill proceeds to deepen the well bore.

PEPTIZATION- An increased dispersion due to the addition of electrolytes or other chemical substances. See Deflocculation and Dispersion.

PEPTIZED CLAY- A clay to which an agent has been added to increase its initial yield. For example, soda ash is frequently added to calcium montmorillonite clay.

PERCENT- For weight-percent, see Ppm. Volume-percent is the number of volumetric parts of any liquid or solid constituent per 100 like volumetric parts of the whole. Volume-percent is the most common method of reporting solids, oil, and water contents of drilling fluids.

PER CENT ADDITIVE- The parts of additive per 100 parts of cement either by volume or by weight. Per cent usually refers to percent by weight. If per cent by volume is meant, it should be so stated.

PER CENT WATER- The water content of a cement slurry expressed as parts of water per 100 parts of dry cement by weight. If per cent by volume is meant, it should be so stated.

PERMEABILITY- The property of a solid medium which allows a fluid to flow through its interconnected pore network. A procedure for determining the permeability of hardened cement is given in API RP 10B. Unit of measurement is the darcy or millidarcy (0.001 darcy). The ability of a porous medium to permit passage of fluids through interconnected pore spaces or voids.

- The property of a porous medium which is a measure of the capacity of the medium to transmit fluids within its interconnected pore network. Unit of measurement is the darcy or millicarcy (0.001 darcy). Normal permeability is a measure of ability of a rock to transmit a one-phase fluid under conditions of laminar flow. Unit of permeability is the darcy.

PERSUADER- A big tool for a small job, used to overcome some trouble.

P1- The phenolphthalein alkalinity of the filtrate, reported as the number of milliliters of 0.02 Normal (N/50) acid required per milliliter of filtrate to reach the phenolphthalein end point.

pH- An abbreviation for potential hydrogen ion. The pH numbers range from 0 to 14, with 7 being neutral, and are indices of the acidity (below 7) or alkalinity (above 7) of the fluid. The numbers are a function of the hydrogen ion concentration in gram ionic weights per liter, which, in turn, is a function of the dissociation of water as given by the following expression:

(H)(OH) = K (H2O) H2O- = 1 x 10-u


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- The pH may be expressed as the logarithm (base 10) of the reciprocal (or the negative logarithm) of the hydrogen ion concentration. The pH of a solution offers valuable information as to the immediate acidity or alkalinity, as contrasted to the total acidity or alkalinity (which may be titrated). A numerical value for the degree of acidity or basicity of an aqueous solution. The pH scale extends from 0 through 14. A pH of 7 is neutral. If a solution is acidic, it will have a pH value lower than 7. If it is basic or alkaline, it will have a pH value above 7. The pH scale is useful in evaluating solutions which are only slightly acidic or basic. A 0.1% solution of HC1 will have a pH of 1, while a 1% solution of caustic soda (NaOH) will have a pH of 14. If these dilute solutions of HC1 and NaOH will show these pH values, 15% HC1 or 10% NaOH would be completely off the pH scale.

PHOSPHATE- Certain complex phosphates, usually sodium tetraphosphate (Na6P4O13) and sodium acid pyrophosphate (SAPP, Na2H2P2O7), are used either as mud thinners or for treatment of various forms of calcium and magnesium contamination.

PIG- A scraping tool forced through a flow line or pipe line to clean out wax or other deposits. See Rabbit.

PIG IRON- Slang for any piece of oil field equipment made of iron or steel.

PILOT TESTING- A method of predicting behavior of mud systems by mixing small quantities of mud and mud additives, then testing the results.

PIPE COEFFICIENTS- A factor used in the Hazen-Williams flow formula to correct for roughness of the inside surface of the pipe.

PIPE-LINE OIL- Oil that is in good enough shape to be run into a pipe line.

PIPELINE PIG- A scraping tool forced through a flow line or pipeline to clean the line or test for obstruction.

PLASTIC FLOW- See Plastic Fluid.

PLASTIC FLUID- A complex, non-Newtonian fluid in which the shear force is not proportional to the shear rate. A definite pressure is required to start and maintain movement of the fluid. Plug flow is the initial type of flow and only occurs in plastic fluids. Most drilling muds are plastic fluids. The yield point as determined by direct-indicating viscometer is in excess of zero.

PLASTICITY- The property possessed by some solids, particularly clays and clay slurries, of changing shape or flowing under applied stress without developing shear planes or fractures. Such bodies have yield points, and stress must be applied before movement begins. Beyond the yield point, the rate of movement is proportional to the stress applied, but ceases when the stress is removed. See Fluid.

PLASTIC VISCOSITY- The plastic viscosity is a measure of the internal resistance to fluid flow attributable to the amount, type, and size of solids present in a given fluid. It is expressed as the number of dynes per sq cm of tangential shearing force in excess of the Bingham yield value that will induce a unit rate of shear. This value, expressed in centipoises, is proportional to the slope of the consistency curve determined in the region of laminar flow for materials obeying Bingham’s law of


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Plastic Flow. When using the direct-indicating viscometer, the plastic viscosity is found by subtracting the 300-rpm reading from the 600-rpm reading.

PLUG BACK- To seal off the bottom section of a well bore to prevent the inflow of fluid from that portion of the hole. This permits the inflow of oil and gas from the formations above the section so sealed off, without contamination of fluids below that depth.

PLUG FLOW- The movement of a material as a unit without shearing within the mass. Plug flow is the first type of flow exhibited by a plastic fluid after overcoming the initial force required to produce flow.

PLUGGING MATERIAL- A material used to block off zones while treating or working on other portions of the well. This blocking off may be temporary or permanent.

PLUNGER LIFT- A method of lifting oil using a swab or free piston propelled by compressed gas from the lower end of the tubing string to the surface.

Pm- The phenolphthalein alkalinity of the mud reported as the number of milliliters of 0.02 Normal (N/50) acid required per milliliter of mud.

POISE- The metric unit for measurement of viscosity. Although the viscosity of cement slurries is expressed in poises for convenience, it is recognized that they do not behave as true Newtonian fluids. See Viscosity.

POLYMER- A substance formed by the union of a two or more molecules of the same kind linked end to end into another compound having the same elements in the same proportion but a higher molecular weight and different physical properties, e.g., paraformaldehyde. See Copolymer. The number of simple molecules that unite to form a polymer molecule can be as great as hundreds or thousands. Synthetic polymers we use are such materials as the FR compounds, HYG-1 and HYG-2 (gelling agents for HY-GEL and LOGEL) and the PVC pipe down at the acid terminal. A substance, often synthetic, composed of giant molecules that have been formed by the union of a considerable number of simple molecules with one another. The chemical units occur in a repeating fashion. The number of simple molecules that unite to form a polymer molecule can be as great as hundreds of thousands.

POLYMER DERIVATIVE- A new and different polymer made by man from an already existing polymer.

POLYMER FLOODING- The displacement of oil by water containing a thickening agent, usually a polysaccharide or polyacrylamide polymer.

POLYSACCHARIDE- A polymer containing repeating sugar units.

POOL- The oil accumulation from which a well or group of wells produce.

POROSITY- The amount of void space in a formation rock, usually expressed as percent voids per bulk volume. In potentially productive zones, this void space is partially or wholly filled with oil, water or gas (or mixtures of these). If the porosity, or void spaces, occur between sand grains, it is called intergranular


55 HRD Standards

porosity. If it occurs as the voids represented by fractures or vugs, it is called fracture porosity or vugular porosity. Porosity is expressed as %.

- Absolute porosity refers to the total amount of pore space in a rock, regardless of whether or not that space is accessible to fluid penetration. Effective porosity refers to the amount of connected pore spaces, i.e., the space available to fluid penetration. See Permeability.

PORTLAND CEMENT CLINKER- Hard granular nodules composed essentially of hydraulic calcium silicates, with smaller quantities of calcium aluminates and ferrites, produced by the heat treatment of cement raw materials in a kiln. Clinker is pulverized with the proper quantity of gypsum in the manufacture of portland cements.

POST-IGNITION PERFORMANCE- The production performance of wells in an in-situ combustion project after ignition of the fire front in the reservoir.

POTASSIUM- One of the alkali metal elements with a valence of 1 and an atomic weight of about 39. Potassium compounds, most commonly potassium hydroxide (KOH) are sometimes added to drilling fluids to impart special properties, usually inhibition.

POTENTIAL- A measure of the capacity of a well to produce oil or gas. When a well is completed, its productive capacity is determined by an official test. The capacity as shown by this test is known as the well’s potential. The allowable rate of production assigned to the well is based in whole or in part on its potential.

POTENTIAL TEST- A test of the maximum rate at which a well can produce oil.

POUND EQUIVALENT- A laboratory unit used in pilot testing. One gram or pound equivalent, when added to 350 ml of fluid, is equivalent to 1 lb/bbl.

POUR POINT- The lowest temperature at which a liquid will flow when a test container (like a test tube) is tilted.

POWER TOOLS- Equipment operated hydraulically or by compressed air for making up and breaking out drill pipe, casing, tubing, and rods.

POZZOLAN- A siliceous or siliceous and aluminous material, which in itself posseses little or no cementitious value but will in finely-divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties. See ASTM C340: Portlant-Pozzoland Cement. Archaic Pozzolana.

POZZOLAN-CEMENT MIXTURE- A mixture comprising both cement and a pozzolan.

POZZOLANIC REACTION- The chemical combination of certain finley divided siliceous or siliceous and aluminous materials with calcium hydroxide or lime, in the presence of moisture, to form compounds that have cementitious properties.

Ppm or PARTS PER MILLION- Unit weight of solute per million unit weights of solution (solute plus solvent), corresponding to weight-percent except that the basis is a million instead of a hundred. The results of standard API titrations of chloride,


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hardness, etc, are correctly expressed in milligrams (mg) of unknown per liter but not in ppm. At low concentrations, mg/l is about numerically equal to ppm. A correction for the solution specific gravity or density in g/ml must be made as follows:

ppm = mg/l _- soln den, g/ml

% by wt. = mg/l _- (10,000) (soln den, g/ml)

= ppm _- 10,000

- Thus, 316,000 mg/l salt is commonly called 316,000 ppm or 31.6 percent, which correctly should be 264,000 ppm and 26.4 percent, respectively.

PRECIPITATE- Material that separates out of solution or slurry as a solid. Precipitation of solids in a drilling fluid may follow flocculation or coagulation, such as the dispersed red-bed clays upon addition of a flocculation agent to the fluid. An insoluble solid substance produced as a result of a chemical reaction.

PRESERVATIVE- Usually paraformaldehyde. Any material used to prevent starch or any other substance from fermenting through bacterial action.

PRESSURE- Force per unit area.

- Bottom Hole Circulating Pressure - The pressure at the bottom of a well during circulation of any fluid. It is equal to the hydrostatic head plus the annular friction loss required to pump the fluid to the surface plus any back pressure held at the surface.

- Bottom Hole Static Pressure - The pressure at the bottom of a well after the well is shut-in long enough to reflect ambient formation pressure.

- Circulating Pressure - The pressure at a specified depth required to circulate a fluid in a well at a given rate.

- Final Squeeze Pressure - The pressure at the completion of a squeeze cementing operation. Final squeeze pressure usually refers to the surface pressure.

- Surface Pressure - The pressure measured at the wellhead.

PRESSURE DECLINE TEST- A minifracturing test in which a well is injected with the treatment fluid at the planned treatment rate, then shut in. The instantaneous shut-in pressure is yielded. The pressure decline data is analyzed using a computer to predict fracturing fluid efficiency, fracture width and fracture length.

PRESSURE-DROP LOSS- The pressure lost in a pipeline or annulus due to the velocity of the liquid in the pipeline, the properties of the fluid, the condition of the pipe wall, and the alignment of the pipe. In certain mud-mixing systems, the loss of head can be substantial.

PRESSURE MAINTENANCE- An improved recovery method utilizing fluid injection to maintain reservoir pressure at a level above that of normal pressure depletion.


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PRESSURE REGULATOR- A valve which controls pressure in a line, downstream from the valve.

PRESSURE SURGE- A sudden, usually short-duration increase in pressure. When pipe or casing is run into a hole too rapidly, an increase in the hydrostatic pressure results, which may be great enough to create lost circulation.

PRIMARY CEMENTING- Primary casing cementing is the original cementing operation performed immediately after casing has been run into the hole. See Casing Cementing.

PRIMARY RECOVERY- The oil or gas recovery obtainable by means of the natural energy mechanisms alone.

PRIME MOVER- As applied to oil well drilling, this is the steam engine, diesel drive, electric motor or internal-combustion engine which is the source of power for the drilling rig.

PRODUCTIVITY TEST- A test of a well’s capacity to produce, usually conducted a different pumping rates or rates of flow. See Potential Test.

PRORATION- A system enforced by the state or by agreement between operators which limits the amount of oil which can be produced from a particular well or field within a given period.

PROTECTION CASING- A string of casing set to protect a section of the hole and to permit drilling to continue to a greater depth. Sometimes called “protection string” and “intermediate string.”

PSEUDOPLASTIC FLUID- A complex non-Newtonian fluid that does not possess thixotropy. A pressure or force in excess of zero will start fluid flow. The apparent viscosity or consistency decreases instantaneously with increasing rate of shear until at a given point the viscosity becomes constant. The yield point is determined by direct-indicating viscometer is positive, the same as in Bingham plastic fluids; however, the true yield point is zero. An example of a pseudoplastic fluid is guar gum in fresh or salt water.

PUDDLING- In cement evaluation work, the term applies to agitation of cement slurry in molds with a rod, to remove any trapped air bubbles. In field practice, the term has been used to denote the reciprocation or rotation of the casing during or after a cementing operation.

PUMP-IN/FLOWBACK TEST- A test in the minifracturing series with an injection rate varying from a minimum of 3 to 5 barrels per minute up to the proposed injection rate at which the fracturing treatment is to be performed. Flowback rates vary from .25 to 1 bbl/min. The closure pressure may be obtained from the pressure inflexion during the flowback portion of this test.

PUMP-IN LEAK-OFF FACTOR- The time (identified by Shelley) necessary to dissipate 200 psi starting one minute after shut-in. This is used for correlating to average treatment parameters.

PUMP-IN/SHUT-IN TEST- See Pressure Decline Test.


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PUMP OFF- To pump so rapidly that the oil level drops below the standing valve on the pump.

PUMPABILITY- A measure of the properties of a fluid or cement slurry to be pumped.

PUMPING TIME- Synonymous with cementing time except in those instances where a volume of cement slurry is premixed prior to displacement in a well. In this instance, the pumping time will be total cementing time minus mixing time.

PULLING CASING- Removing casing from a well.

PUT A WELL ON- To start a well flowing or pumping.

PUT ON PUMP- To install a pump jack or pumping unit, sucker rods, and bottom-hole pump.

QUEBRACHO- A drilling-fluid additive used extensively for thinning or dispersing to control viscosity and thixotorpy. It is a crystalline extract of the quebracho tree consisting essentially of tannic acid.

QUICKLIME- Calcium oxide, CaO. Used in certain oil-base muds to neutralize the organic acid.

QUIESCENCE- The state of being quiet or at rest (being still). Static.

RABBIT- A small plug that is run through a flow line by pressure to clean the line or test for obstructions. See Pig.

RACKING PIPE- The act of placing stands of pipe in orderly arrangement in the derrick while hoisting pipe from the well bore.

RADICAL- Two or more atoms behaving as a single chemical unit, i.e., as an atom; e.g., sulfate, phosphate, nitrate.

RATE OF SHEAR- The rate at which an action, resulting from applied forces, causes or tends to cause two adjacent parts of a body to slide relatively to each other in a direction parallel to their plane of contact. Commonly given in rpm.

REAMING- During drilling operations the sides of the bit become worn with a resulting tendency to drill a well bore smaller than was originally intended. Reaming is the operation employed to enlarge the hole to the size originally planned.

RED MUD- A clay, water-base drilling fluid containing sufficient amounts of caustic soda and tannates to give a pronounced red appearance. Normally a high-pH mud.

RED-LIME MUD- A red mud which has been converted to a lime-treated mud. The pH is usually 12.0 to 13.0.

RELATIVE PERMEABILITY- The ratio of the effective permeability of a fluid to the absolute permeability of the porous medium.


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RELATIVE PERMEABILITY RATIO- The ratio of the relative permeabilities of two fluids, or the ratio of two effective permeabilities.

RELIEF VALVE- A valve that will open automatically when pressure gets to high.

RESERVOIR- Each separate, unconnected body of producing formation.

RESIDUAL OIL SATURATION- The oil left in the pores of a rock through which a displacing fluid has moved; the saturation at which oil ceases to flow.

RESIN- Semisolid or solid complex, amorphous mixture of organic compounds having no definite melting point nor tendency to crystalize. Resin may be a component of compounded materials that can be added to drilling fluids to impart special properties to the system, wall cake, etc.

RESISTIVITY- The electrical resistance offered to the passage of a current, expressed in ohm-meters; the reciprocal of conductivity. Fresh-water muds are usually characterized by high resistivity, salt-water muds by a low resistivity.

RESISTIVITY METER- An instrument for measuring the resistivity of drilling fluids and their cakes.

RETARDER- A chemical which is added to cements to increase their thickening time. A chemical or physical modification that slows the reaction of an acid on the formation so as to achieve deeper penetration.

RETROGRADE CONDENSATE- A condensate reservoir fluid with increasing liquid condensation as pressure declines.

REVERSE CIRCULATE- The method by which the normal flow of a drilling fluid is reversed by circulating down the annulus and up and out the drill string.

REYNOLDS NUMBER- A dimensionless number. RE, that occurs in the theory of fluid dynamics. The diameter, velocity, density and viscosity (consistent units) for a fluid flowing through a cylindrical conductor are related as follows:

- Re = (diameter)(velocity)(density)/(viscosity) or = DVp/u.

- The number is important in fluid hydraulics calculations for determining the type of fluid flow, i.e., whither laminar or turbulent. The transistional range occurs approximately from 2,000 to 3,000; below 2,000 the flow is laminar, above 3,000 the flow is turbulent.

RHEOLOGY- The science that deals with deformation and flow of matter.

RIG, JACKKNIFE OR FOLDING MAST- The type mast that can be folded for moving, as contrasted with the standard derrick, which has to be completely dismantled and re-erected.

RIGGING UP- Before the work of drilling can be started, but after the derrick has been built, tools and machinery must be installed and a supply of fuel and water must be established. This operation, which in substance is that of getting the rig ready, is conveniently described by the driller’s term “rigging up.”

RISER- A pipe through which liquid travels upward.


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ROCK A WELL- To bleed pressure from casing of a dead well, then from tubing, then from casing, and so on so that the well will start to flow.

ROCK PRESSURE- A term used for the initial pressure of gas in a well.

ROTARY DRILLING- The hydraulic process of drilling consists of rotating a column of drill pipe, to the bottom of which is attached a rotary drilling bit, and during the operation, circulating through the pipe a current of mud-laden fluid, under pressure, by means of special slush pumps.

ROUGHNECK- A driller’s helper and general all-around worker on a drilling rig.

ROUSTABOUT- A laborer who assists the foreman in the general work about producing oil wells and around the property of the oil company. The roustabout is a semi-skilled laborer in that he requires considerable training to fit him for his work.

ROYALTY- That part of oil, gas or minerals paid by the lessee to the lessor or to one who has acquired possession of the royalty rights, based on certain percentage of the gross production from the property. Royalty rights can be bought independently of the surface rights. The royalty often amounts to one-eighth of the gross production, but it can be some other amount, depending upon the terms of the lease.

RUN A TANK- To empty oil from a tank into a pipe line.

SACK- Sack is a weight measure. Cement, bentonite, and barite are marketed in sacks containing amounts as follows:

- Cement- 94 pounds

- Bentonite- 100 pounds

- Barite- 100 pounds

SADDLE BEARING- A bearing between the walking beam and the sampson post of a pump jack or pumping unit.

SAFETY JOINT- A special joint used in drilling which can be unscrewed should the tool become stuck in the hole.

SALT- In mud terminology, the term salt is applied to sodium chloride, NaCl. Chemically, the term salt is also applied to any one of a class of similar compounds formed when the acid hydrogen of an acid is partly or wholly replaced by a metal or a metallic radical. Salts are formed by the action of acids on metals, or oxides and hydroxides, directly with ammonia, and in other ways.

SALT-WATER CLAY- See Attapulgite Clay.

SALT-WATER MUDS- A drilling fluid containing dissolved salt (brackish to saturated). These fluids may also include native solids, oil, and/or such commercial additives as clays, starch, etc.

SAMPLE MUD- A drilling fluid possessing properties to bring up suitable samples.


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SAMPLES- Cuttings obtained for geological information from the drilling fluid as it emerges from the hole. They are washed, dried, and labeled as to the depth.

SAND- A loose granular material resulting from the disintegration of rocks, most often silica.

SAND CONTENT- The sand content of a drilling fluid is the insoluble abrasive solids content rejected by a 200-mesh screen. It is usually expressed as the percentage bulk volume of sand in a drilling fluid. This test is an elementary type in that the retained solids are not necessarily silica nor may not be altogether abrasive. For additional information concerning the kinds of solids retained on the 200-mesh screen, more specific tests would be required. See Mesh.

SANDED UP- Clogged by sand entering the well bore with the oil.

SATURATED SOLUTION- A solution is saturated if it contains at a given temperature as much of a solute as it can retain. At 68 F it takes 126.5 lb/bbl salt to saturate 1 bbl of fresh water. See Supersaturated.

SATURATION- The ratio of a fluid volume to the total pore volume in which it resides. Total oil, gas, and water saturation in a rock is always 100%.

SATURATION PRESSURE- See bubble-point pressure.

SCHLUMBERGER- Refers to electric well logging. It is derived from the name of a French scientist who first developed well logging. One of the leading companies in this field of operation bears this name. Around drilling rigs throughout the country it is pronounced “slumberjay.”

SCRAPER- A device used to clean deposits of paraffin from tubing or flow lines.

SCRATCHER- A device fastened to casing which removes the mud cake from the hole to condition it for cementing. It is fashioned of stiff wire.

SCRATCHER TRAP- A trap for inserting or removing a scraper, or “pipeline pig,” from a pipeline. The pig is forced through the line for cleaning or testing for obstructions.

SCREEN ANALYSIS- Determination of the relative percentages of substances, e.g., the suspended solids of a drilling fluid, passing through or retained on a sequence of screens of decreasing mesh size. Analysis may be by wet or dry methods. Referred to also as “sieve analysis.” See Mesh.

SEALING AGENTS- Any of many materials added to drilling fluids to restore circulation.

SEA-WATER MUDS- A special class of salt-water muds where sea water is used as the fluid phase.

SECONDARY RECOVERY- Oil recovery obtained after the end of primary by means of fluid injection.

SECONDS API- A unit of viscosity as measured with a Marsh funnel according to API procedure. See API RP 13B and Marsh Funnel Viscosity.


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SEGREGATION DRIVE RESERVOIR- See gas-cap drive reservoir.

SEISMOGRAPH- A device for detecting vibrations in the earth. It is used in prospecting for probable oil-bearing structures. In this application the vibrations are created by discharging explosives in shallow bore holes. The nature and velocity of the vibrations as recorded by the seismograph indicate the general nature of the section of earth through which the vibrations pass.

SEQUESTER- The action of a chemical to prevent an ion from exhibiting its usual properties. In our work, usually used in reference to preventing an ion from precipitating. Example would be the action of Fe-1A and citric acid to prevent the precipitation of iron ions from spent Fe Acid or MOD Acid. Another example would be the action of scale inhibitors in preventing the precipitation of calcium ions. Typical sequestering agents are polyphosphates, polyacrylates and organic polycarboxylic acids.

SEQUESTRATION- The formation of stable calcium, magnesium, iron complex by treating water or mud with certain complex phosphates.

SET CASING- To install steel pipe or casing in a well bore. An accompanying operation is the cementing of the casing in place by surrounding it with a wall of cement extending for all or part of the depth of the well.

SETTING TIME- A term defining the hardening time of construction cement. This term is not normally used with reference to oil-well cement.

SETTLED PRODUCTION- A loose term used to describe oil fields that produce at nearly the same rate from day to day.

SETTLING- Separation of particles because of different sizes and specific gravities.

SETTLING VELOCITY- The velocity at which a particle of particular size, type, specific gravity, and concentration will settle in a fluid of a particular specific gravity and viscosity. It is usually measured in millimeters per second.

SHACKLE LINE- A pull-rod line.

SHAKE OUT- To spin a sample of oil at high speed to determine its BS&W content.

SHALE- Fine-grained clay rock with slate-like cleavage, sometimes containing an organic oil-yielding substance.

SHALE SHAKER- Any of several mechanical devices for removing cuttings and other large solids from the mud. Common examples are vibrating screen, rotating cylindrical screen, etc.

SHARPSHOOTER- A long, narrow shovel used in ditch digging.

SHEAR (SHEARING STRESS)- An action, resulting from applied forces, which causes or tends to cause two contiguous parts of a body to slide relatively to each other in a direction parallel to their plane of contact.


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SHEAROMETER- A device used as an alternative method for measuring gel strengths. See API RP 13B for specifications and procedure.

SHEAR STRENGTH- A measure of the shear value of the fluid. The minimum shearing stress that will produce permanent deformation. See Gel Strength.

SHEAVE- A grooved pulley.

SHOOTING- Exploding nitroglycerine or other high explosives in a hole to shatter the rock and increase the flow of oil. Same as torpedoing. Also, in seismograph work this refers to the discharge of explosives to create vibrations in the earth’s crust. See Seismograph.

SHOT- A charge of high explosive, usually nitroglycerine, deposited in a well to shatter the sand and to expedite the recovery of oil.

SHUTDOWN- A term denoting that work has been temporarily stopped, as on an oil well.

SHUT IN- To close valves on a well so that it stops producing; said of a well on which the valves are closed.

SHUT-IN PRESSURE- Pressure at the top of a well when it is shut in.

SIDE IRONS- The housing and supports for the bearings of a walking beam.

SIDE TRACKING- Drilling past a broken drill or casing which has become permanently lodged in the hole. This operation is usually accomplished by use of a special tool known as a whip-stock.

SIDE WALL CORING- The taking of geological samples of the formation which constitutes the wall of the well bore. Another term in general use for this operation is “side wall sampling.”

SIEVE ANALYSIS- See Screen Analysis.

SILICA GEL- A porous substance consisting of SiO2. Used on occasion as a dehydrating agent in air or gas drilling where small amount of water is encountered.

SILICA FLOUR- Silica (SiO2) ground to a fineness equal to portland cement. The fineness of portland cement is specified in API Std 10A.

SILT- Materials that exhibit little or no swelling whose particle size generally falls between 2 microns and API sand size, or 74 microns (200-mesh). A certain portion of dispersed clays and barite for the most part also fall into this same particle-size range.

SINGLE- A joint of drill pipe. See Double, Thribble, Fourble.

SKID- Moving a rig from one location to another, usually on tracks where little dismantling is required.

SKIDDING THE RIG- Moving a rig from the location of a lost or completed hole preparatory to starting a new one. In skidding the rig, the move is accomplished with little or no dismantling of equipment.


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SLACK OFF- To lower a load or ease up on a line.

SLING- A wire-rope loop for use in lifting heavy equipment.

SLIPS- Wedge-shaped toothed pieces of metal that fit inside a bowl and are used to support tubing or other pipe.

SLIP VELOCITY- The difference between the annular velocity of the fluid and the rate at which a cutting is removed from the hole.

SLOUGHING- The partial or complete collapse of the walls of a hole resulting from incompetent, unconsolidated formations, high angle or repose, and wetting along internal bedding planes. See Heaving and Cave-in.

SLUG THE PIPE- Before hoisting drill pipe, it is desirable to pump into the top section of a quantity of very heavy mud which will cause the level of the fluid in the pipe to fall. When a stand of pipe is unscrewed the drilling fluid will have been evacuated from it. This prevents crew members and tools from becoming covered with the drilling fluid.

SLURRY- Suspension of cement in water, oil, or mixture of both.

SLURRY VOLUME- The sum of the absolute volumes of solids and liquids that constitute a slurry.

SLURRY DENSITY- The density of a cement slurry expressed in either pounds per gallon or pounds per cubic foot. Light-weight and heavy-weight slurries are prepared by adding suitable additives to modify slurry density.

SLURRY WEIGHT- See Slurry Density.

SLURRY YIELD- (a) Volume of slurry when one sack of cement (94 pounds) is mixed with desired amount of water containing any other additive such as accelerators, fluid-loss control agents, etc. (b) Slurry volume as previously defined by the total number of sacks of cement (94 pounds per sack).

SNAKE OUT- To pull out.

SNATCH BLOCK- A block that can be opened up for putting a line over the roller or sheave.

SOAP- The sodium or potassium salt of high-molecular-weight fatty acid. When containing some metal other than sodium or potassium, they are called “metallic” soaps. Soaps are commonly used in drilling fluids to improve lubrication, emulsification, sample size, defoaming, etc.

SODA ASH- See Sodium Carbonate.

SODIUM- One of the alkali metal elements with a valence of 1 and an atomic weight of about 23. Numerous sodium compounds (see below) are used as additives to drilling fluids.

SODIUM BICARBONATE- NaHCO3. A material used extensively for treating contamination and occasionally other calcium contamination in drilling fluids. It is the half-neutralized sodium salt of carbonic acid.


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SODIUM BICHROMATE- Na2Cr2O7. Also correctly called “sodium dichromate.” See Chromate.

SODIUM CARBONATE- Na2CO3. A material used extensively for treating out various types of calcium contamination. It is commonly called “soda ash.” When sodium carbonate is added to a fluid, it increases the pH of the fluid by hydrolysis. Sodium carbonate can be added to sale (NaCl) water to increase the density of the fluid phase.

SODIUM CARBOXY-METHYLCELLULOSE- Commonly called CMC. A non-fermenting cellulose product used in drilling fluids to combat contamination from anhydrite (gyp), and lower the water loss from the drilling fluid to the formation. Water with more than 20,000 ppm of salt (sodium chloride), reduces its effectiveness as a treating agent.

SODIUM CHLORIDE- NaCl. Commonly known as salt. Salt may be present in the mud as a contaminant or may be added for any of several reasons. See Salt.

SODIUM CHROMATE- Na2CrO4. See Chromate.

SODIUM HYDROXIDE- NaOH. Commonly referred to as “caustic” or “caustic soda.” A chemical used primarily to impart a higher pH.

SODIUM POLYACRYLATE- A synthetic high-molecular-weight polymer of acrylonitrile used primarily as a fluid-loss-control agent.

SODIUM SILICATE MUDS- Special class of inhibited chemical muds using as their bases sodium silicate, salt, water, and clay.

SOFT ROPE- A small loose fiber rope.

SOL- A general term for colloidal dispersions, as distinguished from true solutions.

SOLIDS CONCENTRATION OR CONTENT- The total amount of solids in a drilling fluid as determined by distillation includes both the dissolved and the suspended or undissolved solids. The suspended-solids content may be a combination of high and low specific gravity solids and native or commercial solids. Examples of dissolved solids are the soluble salts of sodium, calcium, and magnesium. Suspended solids make up the wall cake; dissolved solids remain in the filtrate. The total suspended and dissolved solids contents are commonly expressed as percent by volume, and less commonly as percent by weight.

SOLUBILITY- The amount or percent of a material that dissolves in a certain fluid. For example, if 1.00 grams of a core was ground up and placed in excess HC1, and after several hours the remaining material was filtered out, dried, weighed, and found to weight 0.70 grams, the soluble portion would be 0.30 gram or 30% soluble in HC1. The degree to which a substance will dissolve in a particular solvent.

SOLUTE- A substance which is dissolved in another (the solvent).

SOLUTION- A mixture of two or more components that form a homogeneous single phase. Example solutions are solids dissolved in liquid, liquid in liquid, gas in liquid.

SOLUTION GAS DRIVE RESERVOIR- See depletion drive reservoir.


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SOLUTION GAS-OIL RATIO- The equivalent standard volume of gas in solution in the oil in the reservoir per unit volume of stock-tank oil.

SOLVENT- Liquid used to dissolve a substance (the solute).

SOUR GAS- Gas that smells bad because of impurities, usually hydrogen sulfide.

SOURING- A term commonly used to mean fermentation (which see).

SPACING- Distance between wells producing from the same pool (usually expressed in terms of acres, e.g., 10-acre spacing).

SPAGHETTI- Very small tubing or pipe.

SPECIFIC GRAVITY- The weight of any volume of a material divided by the weight of the same volume of a material taken as a standard. For solids or liquids, the standard is water. For gases, the standard is air. It may also be defined as the ratio of the density of a substance to the density of water or air. We deal mostly with liquids and solids. The density of water is 1 gm/cc or 8.33 lb/gal. To go from density to specific gravity, and vice versa, is a simple matter. For example, given a 10 lb/gal brine, calculate its specific gravity:

- 10 lb/gal Specific Gravity = 8.33 lb/gal = 1.2

- Suppose you are given the specific gravity of a liquid as 1.2. Calculate the density: 1.2 × 8.33 lb/gal; = 10 lb/gal. See Gravity, Specific.

SPECIFIC HEAT- The number of calories required to raise 1 g of a substance 1 deg Centigrade. The specific heat of a drilling fluid gives an indication of the fluid’s ability to keep the bit cool for a given circulation rate.

SPECIFIC PERMEABILITY See absolute permeability.

SPENDING- The reaction of an acid with another substance which uses up the hydrogen (H+) ions and, therefore, decreases the strength of the acid.

SPINNER SURVEY- An operation designed to indicate the point at which fluids are escaping from the well bore into a cavernous or porous formation.

SPUDDING- Refers to the acting of hoisting the drill pipe and permitting it to fall freely so that the drill bit strikes the bottom of the well bore with considerable force. This is done to clean the bit of an accumulation of sticky shale that has slowed down the rate of penetration. Careless execution of this operation can result in kinks in the drill pipe and damaged bits.

SPUDDING IN- The very beginning of drilling operations of a well. The term has been handed down from cable tool operations in the early days of the oil industry.

SPUD MUD- The fluid used when drilling starts at the surface, often a thick bentonite-lime slurry.

SPURT LOSS- See Surge Loss.

SQUEALER- A noise maker attached to the end of an exhaust pipe.


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SQUEEZE- A procedure whereby slurries of cement, mud, gunk plug, etc. are forced into the formation by pumping into the hole while maintaining a back pressure, usually by closing the rams.

SQUEEZE CEMENTING- The process of forcing cementing material under pressure into a specific portion of a well, such as fractures, openings, or permeable zones.

- High Pressure Squeeze Cementing - The forcing of cement slurry into the points to be squeezed with a final pressure equal to or greater than the formation breakdown pressure.

- Low Pressure Squeeze Cementing - The forcing of cement slurry into the points to be squeezed with a pressure not exceeding the formation breakdown pressure.

SOUNDNESS- A measure of the expansive properties of a cement as determined by the autoclave expansion test given in ASTM C 151: Test for Autoclave Expansion of Portland Cement.

STAB- To guide the end of a pipe into a coupling when making up a connection.

STABBING BOARD- A temporary platform erected in the derrick at an elevation of about 20 to 40 feet above the derrick floor. The derrickman or other crew member works on this board while casing is being run in a well. Derived from the term “to stab” meaning to guide a joint while it is being screwed into another joint or section.

STABILITY METER- An instrument to measure the breakdown voltage of invert emulsions.

STABILIZED- A well is considered “stabilized” when, in the case of a flowing well, the rate of production through a given size of choke remains constant, or, in the case of a pumping well, when the fluid column within the well remains constant in height.

STACKING A RIG- Storing a drilling rig upon completion of a job when the rig is to be withdrawn from operation for a period of time.

STAND IT ON THE BOARDS- To bring the pipe out of the hole (make a trip) and rack it in the derrick.

STAND OF PIPE- Two or three or sometimes four joints of pipe fastened together, called a double, thribble, or fourble, respectively.

STARCH- A group of carbohydrates occurring in many plant cells. Starch is specially processed (pregelatinized) for use in muds to reduce filtration rate and occasionally to increase the viscosity. Without proper protection, starch can ferment.

STATIC- Opposite of dynamic. See Quiescence.

STEADY-STATE PHASE FLOW- An equation of flow in which time is assumed to have no significance.


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STEAM DISTILLATION- The removal of lighter hydrocarbons from a crude oil by passing steam through or over the oil.

STEAM RIG- A drilling rig whose source of power is a battery of portable boilers.

STEARATE- Salt of stearic acid, which is a saturated, 18-carbon fatty acid. Certain compounds, such as aluminum stearate, calcium stearate, zinc stearate, have been used in drilling fluids for one or more of the following purposes: defoamer, lubrication, air drilling in which a small amount of water is encountered, etc.

STEP RATE TEST- A minifracturing test performed to obtain the fracture extension pressure. The test is usually performed by pressuring a well at constant rate increments (example: 0.5, 1.0, 1.5, ...5 barrels per minute) and plotting the maximum pressure at each step vs. the constant rate at each stop. The inflexion point corresponds to the fracture extension pressure.

STRATIFICATION- The natural layering or lamination usually characteristic of sediments and sedimentary rocks. Stratification is the result of the settling of particles of different sizes and specific gravities.

STREAMING POTENTIAL- The electrokinetic portion of the SP (spontaneous potential) electric-log curve which can be significantly influenced by the characteristics of the filtrate and mud cake of the drilling fluid that was used to drill the well.

STREAMLINE FLOW- See Laminar Flow.

STRENGTH RETROGRESSION- The decline of strength of the hardened cement slurry with age, which may occur at temperatures above 180°F.

STRIKE- The direction of the line formed by intersection of a bedding or fault plane with the horizontal plane.

STRINGING-UP- The act of threading the drilling line through the sheaves of the traveling block and the crown block. One end of the line is secured to the hoisting drum and the other anchored to the derrick substructure. See Fast Line, Dead Line.

STRIP A WELL- To pull rods and tubing from a well at the same time. Tubing must be “stripped” over the rods a joint at a time.

STRIPPER- A well which produces a very small amount of oil, usually in and old field.

STROMATOPOROID- A type of calcareous algae forming bulbous or laminar structures.

STROMATOLITE- A mat or mound of stromatoporoidal algae, platelike or tabular in structure.

STRUCTURAL CONTOURS- Contour lines which represent the structure or shape of the surface of a given rock bed. Lines drawn on a map representing lines of elevation.

STRUCTURE- An underground geological feature capable of forming a reservoir for oil and gas.


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STRUNG UP- To have rigged up wire rope and sheaves or blocks for hoisting.

STUCK- Refers to the drill pipe or casing inadvertently becoming fastened in the hole. May occur while drilling is in progress, while casing is being run in the hole or while the drill pipe is being hoisted. Frequently results in a fishing job.

STYLOLITE- A small columnar development in limestones or other calcareous rocks that runs across the stratification.

SUBLIME- To pass directly from a solid to a gaseous state.

SUBSTRUCTURE- The foundation on which the derrick and engines sit. Contains space for storage and well control equipment.

SUITCASE STAND- A formation which has been found to be non-productive of oil and gas. It is derived from the fact that operations are suspended and the crews pack their suitcases and move to another job.

SULFATE RESISTANCE- The ability of a cement to resist deterioration in the presence of sulfate ions.

SUPERCOMPRESSIBILITY FACTOR- See compressibility factor.

SUPERSATURATION- If a solution contains a higher concentration of a solute in a solvent than would normally correspond to its solubility at a given temperature, this constitutes supersaturation. This is an unstable condition, as the excess solute separates when the solution is seeded by introducing a crystal of the solute. The term “supersaturation” is frequently used erroneously for hot salt muds.

SURFACE-ACTIVE MATERIALS- See Surfactant.

SURFACE CONTOURS- Lines of equal elevation drawn on a surface map, resulting in a topographic map.

SURFACE PIPE- The first string of casing to be set in a well. The length will vary in different areas from a few hundred feet to three or four thousand feet. Some states require a minimum length to protect fresh-water sands. On some wells it is necessary to set a temporary conductor pipe which should not be confused with surface pipe as described here.

SURFACE TENSION- The forces existing in the surface film of all liquids which tends to contract the volume into a form with the least surface area. This would be a sphere, or a round droplet. The particles in the surface film are inwardly attracted thus resulting in tension. Generally, the force acting within the interface between a liquid and its own vapor, which tends to maintain the area of the surface at a minimum and is expressed in dynes per centimeter. Since the surface tension of a liquid is approximately equal to the interfacial tension between the liquid and air, it is common practice to refer to values measured against air as surface tension, and to use the term “interfacial tension” for measurements at an interface between two liquids, or a liquid and a solid. Mercury has a very strong surface tension, so it always tends to form balls of itself. Water has strong surface tension and also tends to form balls, especially in contact with oil surfaces. Alcohol and the common liquid hydrocarbons which we deal with (Paragon, kerosene, diesel oil, gasoline) have low surface tensions and tend to spread out on a solid surface to form a film.


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The surface tension of most liquids can be changed by the addition of proper chemicals. The tension results from unbalanced intermolecular forces at the surface and produces a thin, skin-like layer of molecules. Mercury has a very strong surface tension, so it always tends to form balls of itself. Water has a strong surface tension and also tends to form balls, especially in contact with oily surfaces. Alcohol and the common liquid hydrocarbons have low surface tensions and tend to spread out on a solid surface to form a film. The surface tension of most liquids can be changed by the addition of proper chemicals.

SURFACTANT- In the broadest sense, this can be defined as a “surface active agent.” Or, a chemical which, when added to a liquid, will change the surface tension of the liquid. Practically, we limit the term to those chemicals which lower the surface tension of liquids. A material that raises the surface tension of a liquid we usually call an emulsifier. A material that tends to concentrate at an interface. Used in drilling fluids to control the degree of emulsification, aggregation, dispersion, interfacial tension, foaming, defoaming, wetting, etc. A contraction of “surface active agent.” A surfactant is a chemical which, when added to a liquid, will change the surface tension of the liquid at relatively low concentrations, Practically, we limit the term to those chemicals which lower the surface tension of liquids. A material which raises to surface tension of a liquid is usually called an emulsifier. Surfactants are normally mixtures of complex organic compounds, which, in the pure state, are either solids or very viscous fluids. They are diluted with alcohol or methyl ethyl ketone or similar solvents to a viscosity which can be used over a wide temperature range. Some materials that are not classified as surfactants will lower the surface tension of a liquid. Two of these are alcohol and carbon dioxide. Surfactants normally used in the oil field act by adsorbing on the interface between two liquids, one hydrocarbon and the other and aqueous liquid, or on the surface of a liquid exposed to air. The molecules of these surfactants have an oil soluble end and a water soluble end (hydrophobic) and a water soluble end (hydrophilic). At the interface, the oil soluble end of the molecule is oriented in the hydrocarbon liquid while the water soluble end is in the water or water based liquid. An efficient surfactant will lower the surface tension of a water based to 30 dynes/cm or less, and will lower the interfacial tension between a hydrocarbon and a water based liquid to zero or near zero.

SURFACTANT MUD- A drilling fluid which contains a surfactant. Usually refers to drilling fluid containing surfactant material to effect control over degree of aggregation and dispersion or emulsification.

SURGE LOSS- The flux of fluids and solids which occurs in the initial stages of any filtration before pore openings are bridges and a filter cake is formed. Also called “spurt loss.”

SUSPENSOID- A mixture consisting of finely divided colloidal particles floating in a liquid. The particles are so small that they do not settle but are kept in motion by the moving molecules of the liquid (Brownian movement).

SWAB- A device that fits the inside of tubing closely that is pulled through the tubing to lift fluid from it, or to pull such a device through the tubing.

SWABBING- Operation of a lifting device to bring well fluids to the surface when the well does not flow naturally. This is a temporary operation to determine


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whether or not the well can be made to flow. In the event the well does not flow after being swabbed, it is necessary then to install a pump as a permanent lifting device to bring oil to the surface.

SWAMPER- A helper on a truck.

SWEET- Said of oil or gas when it contains no sour impurities.

SWELLING- See Hydration.

SWIVEL- A hose coupling which forms a connection between the slush pumps and the drill string and permits rotation of the drill string.

SYNCLINE- A trough in the rock beds; a structurally low point toward which the rocks dip; a structural basin.

SYNERGISM, SYNERGISTIC PROPERTIES- Term describing an effect obtained when two or more products are used simultaneously to obtain a certain result. Rather than the results of each product being additive to the other, the result is a multiple of the effects.

SYNGENETIC- Internally generated or controlled. The cooperative action of two or more chemicals that work together to do a better job than either could do alone. Usually this term is used to describe the action of two chemicals that are used for the same purpose.

TAIL CHAIN- A short length of chain attached to the end of a winch line.

TAIL OUT RODS- To pull the bottom end of a sucker rod away from a well when laying rods down.

TAKE A STRAIN ON- To begin to pull on a load.

TALLY- To measure and record length of pipe or tubing.

TALUS- Rock debris on a slope, at the foot of a cliff or below a rock face.

TANK STRAPPER- The person who measures a tank to see how much it will hold at various levels.

TANNIC ACID- Tannic acid is the active ingredient of quebracho and other quebracho substitutes such as mangrove bark, chestnut extract, hemlock, etc.

TAP- A notched tool used to cut inside threads.

TEARING DOWN- The act of dismantling a rig at the completion of a well and preparing it for moving to the next location.

TECTONIC- Pertaining to the rock structures and external forms resulting from the deformation of the earth’s crust.

TEMPERATURE- The degree of heat, usually expressed as degrees fahrenheit.

- Bottom Hole Circulating Temperature - The temperature of any fluid at the bottom of the well while it is being circulated.


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- Bottom Hole Static Temperature - The temperature attained at the bottom of a well after the well is shut-in. See Static Temperature.

- Casing Cementing Temperature - The temperature of a cement slurry while it is being displaced at the maximum cementing depth in a casing cementing operation.

- Circulating Temperature - The temperature of any fluid at any specified depth in well while it is being circulated, as measured inside casing or drill pipe.

- Squeeze Cementing Temperature - The temperature of a cement slurry while it is being displaced at the maximum cementing depth in a squeeze cementing operation.

- Static Temperature - The temperature attained at a specified depth in a well after the well is shut-in long enough to reflect the ambient formation temperature.

TEMPERATURE STABILITY- The chemical characteristics of a material which determine its resistance to thermal decomposition.

TEMPERATURE SURVEY- An operation to determine temperatures at various depths in the hole. This survey is used to find the location of inflows of water into the hole, where doubt exists as to proper cementing of the casing and for other reasons.

TENDER- The barge anchored alongside an offshore drilling platform. Usually contains living quarters, storage space, and the mud system.

TEN-MINUTE GEL- See Gel Strength, 10-min.

TENSILE STRENGTH- A measure of force per unit cross sectional area required to pull a specimen apart.

TENSILE STRESS- The perpendicular components of internal stress exert a pull between the two parts of the mass which constitutes a tensile stress. A pull-apart stress.

TERTIARY RECOVERY- Oil recovery obtained after the end of a secondary recovery process, usually by fluid injection.

TERRESTRIAL BEDS- Beds laid down on land.

TERRESTRIAL DEPOSITS- Those accumulations of the mechanical and chemical waste of pre-existent rocks which are formed on land surfaces.

TERRIGENEOUS- Produced from or of the earth; in geology, deposited in or on the earth’s crust.

THERMAL DECOMPOSITION- The chemical breakdown of a compound or substance by temperature into simple substances or into its constituent elements. Starch thermally decomposes in drilling fluids as the temperature approaches 300 F.


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THERMAL RECOVER- The recovery of oil by means of the addition of heat to the reservoir for the purpose of reducing oil viscosity; thereby rendering it more mobile.

THICKENING-TIME- The time required for a cement slurry of a given composition to reach a consistency of 100 Vc. Determined by methods outlined in API RP 10B.

THINNER- Any of various organic agents (tannins, lignins, lignosulfonates, etc.) and inorganic agents (pyrophosphates, tetraphosphates, etc.) that are added to a drilling fluid to reduce the viscosity and/or thixotropic properties.

THIXOTROPY- The property exhibited by certain systems of gelling when in a static state, and then liquefying when subjected to agitation. The ability of fluid to develop gel strength with time. That property of a fluid which causes it to build up a rigid or semirigid gel structure if allowed to stand at rest, yet can be returned to a fluid state by mechanical agitation. This change is reversible.

THRIBBLE- A stand of drill pipe made up of three joints, each about 30 feet in length. This is equivalent to a fourble of 4 joints about 22 feet to 23 feet in length. Setting back fourbles of 30-foot joints requires a taller derrick than is normally used in rotary drilling. See Fourble; Double.

THROWING THE CHAIN- The act of placing several wraps of spinning chain around a section of drill pipe in making a connection. The joint of drill pipe is turned by pulling one end of the spinning chain with power from the cathead.

TIE-DOWN- A device to which a guy wire or brace may be attached.

TIE LINE- A locus of points connection equilibrium vapor and liquid compositions, usually on a ternary diagram.

TIGHTEN UP EMULSION OR MUD- Drilling-fluid jargon to describe condition in some systems to which oil has been added and the oil breaks out and rises to the surface. Any chemical or mechanical means which will emulsify the free oil is known as “tightening up.”

TILTOMETER- A tool that is cemented into the ground and used to measure the ground tilt around a fractured well for determination of fracture azimuth.

TIN HAT- The metal hat worn by oil-field workers to protect them from falling objects.

TITRATION- A method, or the process of using a standard solution for the determination of the amount of some substance in another solution. The known solution is usually added in a definite quantity to the unknown until a reaction is complete.

TOMBOLO- A bar-type sand body connecting two land bodies.

TOOL JOINT- A drill-pipe coupler consisting of a pin and box of various designs and sizes. The internal design of tool joints has an important effect on mud hydrology.


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TOOL PUSHER- A foreman in charge of one or more drilling rigs. Supervisor of drilling operations.

TOPOGRAPHY- The general configuration of the land surface; the sum total of the results of erosion and deposition on the physiographic features of a region.

TORQUE- A measure of the force or effort applied to a shaft, causing it to rotate. On a rotary rig this applies especially to the rotation of the drill stem in its action against the bore of the hole. Torque reduction can usually be accomplished by the addition of various drilling-fluid additives.

TOTAL DEPTH (OR TD)- The greatest depth reached by the drill bit.

TOTAL HARDNESS- See Hardness of Water.

TOTAL PERMEABILITY- See absolute permeability.

TOTAL POROSITY- The ratio of the total void or pore space volume of a rock to its bulk volume.

TOUR- The word which designates the shift of a drilling crew or other oil field workers is pronounced usually as if it were spelled t-o-w-e-r. The word does not refer to the derrick or tower, as some seem to think, the day tour starts at 7 or 8 in the morning. The evening tour starts at 3 or 4 o’clock in the afternoon. The morning tour starts at 11 p.m. or midnight (sometimes referred to as graveyard tour). The almost universal practice in oil well drilling is to work 8-hour tours or shifts.

TRIP- To pull or run a string of rods or tubing from or into a well.

TUBING JOB- The pulling and running of tubing.

TURBIDITY- A measure of the resistance of water to the passage of light through it. It is caused by suspended and colloidal matter in the water.

TURBULENT FLOW- Fluid flow in which the velocity at a given point changes constantly in magnitude and the direction of flow; pursues erratic and continually varying courses. Turbulent flow is the second and final stage of flow in a Newtonian fluid; it is the third and final stage in a Bingham plastic fluid. See Critical Velocity and Reynolds Number.

TURNING TO THE RIGHT- A slang term on a rotary rig referring to the drilling operation during which the drill stem is rotated in a clockwise direction.

TWIST-OFF- The severing in two of a joint of drill pipe by excessive force applied by the rotary table.

ULTRAVIOLET LIGHT- Light waves shorter than the visible blue-violet waves of the spectrum. Crude oil, colored distillates, residuum, a few drilling-fluid additives, and certain minerals and chemicals fluoresce in the presence of ultraviolet light. These substances, when present in mud, may cause the mud to fluoresce.

UNDER-REAM- To enlarge a drill hole below the casing.


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UNIFORMITY COEFFICIENT- A term used in specifying sand. It is the ratio of the sieve size that will pass 60 percent of the filter sand, to the effective size.

UNIT DISPLACEMENT EFFICIENCY- The fractional oil recovery, at a point in the process, by displacement from a unit pore volume of invaded rock.

UNIVALENT- Monovalent. See Valence.

VACUUM- A void; an absence of matter of any kind. Complete vacuum has not yet been attained, but a partial vacuum is achieved in various items of mechanical equipment.

VACUUM GAUGE- An instrument used on drilling engines to indicate their performance characteristics and the load being carried by each.

VALENCE OR VALENCY- The valence is a number representing the combining power of an atom, i.e., the number of electrons lost, gained, or shared by an atom in a compound. It is also a measure of the number of hydrogen atoms with which an atom will combine or replace, e.g., an oxygen atom combines with two hydrogens, hence has a valence of 2. Thus, there are mono-, tri-, etc. valent ions.

VALENCE EFFECT- In general, the higher the valence of an ion, the greater the loss of stability to emulsions, colloidal suspensions, etc. These polyvalent ions will impart.

VAPOR-PROOF- A term used to describe a product that is not susceptible to the action of gases or other vapors. Its principal application on a drilling rig is to describe explosion-proof light fixtures which are safe in the presence of combustible gases.

V-DOOR (WINDOW)- An opening in a side of a derrick at the floor level having the form of an inverted V. This opening is opposite the draw-works. It is used as an entry to bring in drill pipe and casing from the pipe rack.

VELOCITY- Time rate of motion in a given direction and sense. It is a measure of the fluid flow and may be expressed in terms of linear velocity, mass velocity, volumetric velocity, etc. Velocity is one of the factors that contribute to the carrying capacity of a drilling fluid.

VELOCITY, CRITICAL- That velocity at the transitional point between laminar and turbulent types of fluid flow. This point occurs in the transitional range of Reynolds numbers of approximately 2,000 to 3,000.

VERTICAL CONFORMANCE EFFICIENCY- The fractional coverage of a vertical slice of the reservoir by a displacing fluid.

V-G METER OR VISCOSITY GRAVITY VISCOMETER- The name commonly used for the direct-indicating viscometer (which see).

VIBRATING SCREEN- See Shale Shaker.

VISCOMETER (VISCOSIMETER)- An apparatus to determine the viscosity of a fluid or suspension. Viscometers vary considerably in design and methods of testing.


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VISCOMETER, DIRECT-INDICATING- Commonly called a “V-G meter.” The instrument is a rotational-type device powered by means of an electric motor or handcrank, and is used to determine the apparent viscosity, plastic viscosity, yield point, and gel strengths (all of which see) of drilling fluids. The usual speeds are 600 and 300 rpm. See API RP 13B for operational procedures.

VISCOMETER, STORMER- A rotational shear viscometer used for measuring the viscosity and gel strength of drilling fluids. This instrument has been largely superseded by the direct-indicating viscometer (which see).

VISCOSIMETER- See Viscometer.

VISCOSITY- The internal resistance offered by a fluid to flow. This phenomenon is attributable to the attractions between molecules of a liquid, and is a measure of the combined effects of adhesion and cohesion to the effects of suspended particles, and to the liquid environment. The greater this resistance, the greater the viscosity. See Apparent and Plastic Viscosity.

VISCOSITY, FUNNEL- See Funnel Viscosity.

VISCOUS FLOW- See Laminar Flow.

VOLATILE CRUDE OIL- A reservoir oil for which some or all of its physical properties can be defined satisfactorily only in terms of pressure, temperature, and composition.

VOLATILE MATTER- Normally gaseous products, except moisture, given off by a substance, such as gas breaking out of live crude oil that has been added to a mud. In distillation of drilling fluids, the volatile matter is the water, oil, gas, etc., that are vaporized, leaving behind the total solids which can consist of both dissolved and suspended solids.

VOLUMETRIC CONFORMANCE- The fraction of the reservoir pore volume invaded by a displacing fluid (also conforming volume); the multiple of the areal sweep and vertical conformance efficiencies.

VUGS- Natural cavities formed in certain formations due to leaching out of soluble minerals. These cavities are lined with a crystalline material and a composition different from that of the surroundings. The size of a vug may vary from a small pea to a large boulder.

W.O.C.- See Waiting on Cement.

WAITING ON CEMENT- After the casing has been cemented, it is necessary to suspend operations and allow time for the cement to set or harden in the well bore. The time during which operations are suspended is designated as waiting on cement.

WALL CAKE- The solid material deposited along the wall of the hole resulting from filtration of the fluid part of the mud into the formation.

WALL STICKING- See Differential-pressure Sticking.

WARM UP- The same as heat--loosen a connection by hammering on it.


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WATER BASE GELLING AGENT- A polymer which thickens or gels water.

WATER-BASE MUD- Common conventional drilling fluids. Water is the suspending medium for solids and is the continuous phase, whether or not oil is present.

WATER BLOCK- Reduction of the permeability of a formation caused by the invasion of water into the pores (capillaries). The decrease in permeability can be caused by swelling of clays, thereby shutting off the pores, or in some cases by a capillary block of the pores due to surface tension phenomena.

WATER-CEMENT RATIO- The ratio by weight of water to cement in a cement slurry.

WATER DRIVE RESERVOIR- An oil or gas reservoir producing predominantly by the energy derived from water encroachment from an associated aquifer.

WATER-IN-OIL EMULSION- See Invert Oil-emulsion Mud.

WATER LOSS- See Fluid Loss. The volume of water lost to the permeable material due to the process of filtration. The API water loss is the volume of filtrate determined according to the Fluid-Loss Test given in API RP 10B. See Fluid Loss.

- High Water Loss - A cement slurry is arbitrarily considered to exhibit a high water loss when the volume of filtrate determined according to the Fluid Loss Test given in API RP 10B exceeds 500 ml.

- Low Water Loss - A cement slurry is considered low water loss when the volume of filtrate as determined above is less than 50 ml.

- Medium Water Loss - A cement slurry is considered medium water loss when the volume of filtrate as determined above is between 50 and 500 ml.

WATER LOSS CONTROL- To regulate the water loss of a cement slurry by the use of additives.

WATER OF HYDRATION- The water chemically combined with the solid to form a crystalline compound. In cement slurries, the water necessary to hydrate the cement, forming cementitious materials.

WATER-SOLIDS RATIO- The ratio by weight of water to the total solids in a cement slurry.

WATER STRING- A string of casing used to shut off all water above an oil sand. It is often necessary to run more than one string before a well is completed.

WATER TABLE- The underground level at which water is found. This term is often used in connection with underground water supplies used for irrigation and industrial plants. Term also used to designate the top of the drilling derrick which supports the crown block.

WEIGHT- In mud terminology, this refers to the density of a drilling fluid. This is normally expressed in either lb/gal, lb/cu ft, psi hydrostatic pressure per 1,000 ft of depth.


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WEIGHT MATERIAL- Any of the high specific gravity materials used to increase the density of drilling fluids. This material is most commonly barite but can be galena, etc. In special applications limestone is also called a weight material.

WELL SIMULATION TEST- A test performed in accordance with API RP 10B under conditions simulating those encountered in wells.

WELL LOGGING- See Electric Logging and Mud Logging.

WET COMBUSTION- The in-situ combustion process with the injection of air and water simultaneously or in a alternating volumes.

WET GAS- Gas that carries a lot of liquids with it.

WETTING AGENT- A surface active agent which, when added to a liquid, causes it to spread over the surface of, or penetrate more easily into, another material. This usually results from the reduction of surface tension of the liquid and interfacial tension between the two materials.

WETTABILITY REVERSAL The displacement of oil by chemical means which results in a change to the wettability of the oil-water system. An enhanced recovery method.

WETTING- The adhesion of a liquid to the surface of a solid.

WETTING AGENT- A substance or composition which, when added to a liquid, increases the spreading of the liquid on a surface or the penetration of the liquid into a material.

WHIPSTOCK- A device inserted in a well bore used for deflecting or for directional drilling.

WIDOW MAKER- Anything liable to cause death or serious injury of a workman.

WIGGLE STICK- The walking beam.

WILDCAT- A well in unproved territory. With present day exploration methods and equipment about one wildcat of every 10 drilled proves to be commercially productive.

WINCH- A machine used for pulling or hoisting that does so by winding a cable around a spool.

WIND-LOAD RATING- A specification of a derrick used to indicate the resistance of the derrick to the force of wind. The wind loading rating is calculated according to formulas incorporated in A.P.I. specifications. Typical wind resistance of derricks is 75 miles per hour with pipe standing in the derrick and 115 miles per hour and more with no pipe standing in the derrick.

WORKING INTEREST- Portion of oil production out of which operating and development costs are paid.

WORKING PRESSURE- The maximum pressure at which an item is to be used at a specified temperature.


79 HRD Standards

WORK-OVER- To perform one or more of a variety of remedial operations on a producing oil well with the hope of restoring or increasing production. Examples of work-over operations are deepening, plugging back, pulling and resetting the liner, squeeze cementing, shooting, and acidizing.

WORKOVER FLUID- Any type of fluid used in the workover operation of a well.

WORMHOLE- Large, highly conductive channels that result from the matrix reaction of acid with highly reactive sections of the formation. Usually a wormhole starts by enlarging already large permeable vugs or pores and moves forward as it creates additional surface area.

WRINKLE PIPE- To cut threads on a piece of pipe in order to make a connection.

YIELD- A term used to define the quality of clay by describing the number of barrels of a given centipoise slurry that can be made from a ton of the clay. Based on the yield, clays are classified as bentonite, high-yield, low-yield, etc., types of clays. Not related to yield value below. See API RP 13B for procedures.

YIELD POINT- In drilling-fluid terminology, yield point means yield value (which see). Of the two terms, yield point is by far the most commonly used expression.

YIELD VALUE- The shear stress intercept resulting from an extrapolation of higher shear stress-shear rates values to a zero shear rate. The yield value (commonly called “yield point”) is the resistance to initial flow, or represents the stress required to start fluid movement. This resistance is due to electrical charges located on or near the surfaces of the particles. The values of the yield point and thixotropy, respectively, are measurements of the same fluid properties under dynamic and static states. The Bingham yield value, reported in lb/100 sq ft, is determined by the direct-indicating viscometer by subtracting the plastic viscosity from the 300-rpm reading.

YOUNG’S MODULUS- The ratio of stress to strain of a material undergoing elastic strain.

ZERO-ZERO GEL- A condition wherein the drilling fluid fails to form measurable gels during a quiescent time interval (usually 10 min).

ZETA POTENTIAL- Electrokinetic potential of a particle as determined by its electrophoretic mobility. This electric potential causes colloidal particles to repel each other and stay in suspension.

Z-FACTOR- See compressibility factor.

ZINC CHLORIDE- ZnCl2. A very soluble salt used to increase the density of water to points more than double that of water. Normally added to a system first saturated with calcium chloride.

NOMENCLATURE

Symbol- Description- Units

Av- Absolute Volume

- Intermediate Strength Proppant =- 0.0370 gal./lb


80 HRD Standards

- Sand =- 0.0456 gal./lb

BHTP- Bottomhole Treating Pressure- psi

bbl- Barrels - 42 gallons- bbls

BPM- Barrels Per Minute (rate)- bbls/min.

CD- Drag Coefficient- -

Cp (1)- Perforation Coefficient- -

D- Depth- feet

DEF- Equivalent Diameter for Friction- inch

DEV- Equivalent Diameter for Velocity- inch

E- Young’s Modulus

Ez- Axial Strain- -

Er- Lateral Strain- -

Pf- Friction Loss - Pipe- psi

Pf (A)- Friction Loss in Pipe (actual)- psi/100 ft

Pf (B)- Friction Loss From Charts of Data (base)- psi/100 ft

Pfe (2)- Friction Loss - Fracture Entry- psi

Ppf- Friction Loss - Perforations- psi

Ppfo- Friction Loss - Observed at Perforations- psi

Pw- Wellhead Pressure- psi

Do- Internal Diameter of Casing- inch

Dp- Diameter of Perforations- inch

Dt- Outside Diameter of Tubing- inch

Dv- Diameter of Vena Contracta- inch

FD- Fluid Density- lb/gal.

FG- Fracture Gradient- psi/ft

1)- Will vary from 0.80 to 0.95, if unknown use 0.95.

2)- Pfe is fracture entry friction, that is, the friction past the perforation but before the entrance to the fracture. This friction can make the perforation friction erroneous.

Symbol- Description

FT- Temperature of Fluid- Deg F


81 HRD Standards

ft- Feet- ft

HHP- Hydraulic Horsepower- hp

I.D.- Inside Diameter- inch

k- Formation Permeability- md

Kf- Fracture Permeability- md

lb- Pound- lb

M- 1,000 Gallons- M

- Fluid Viscosity- cp

- Fluid Density- lb/cu ft

MR- Modified Rate- BPM, bbl/min

N- Number of Perforations- -

Nre- Reynolds Number- -

O.D.- Outside Diameter- inch

Ph- Hydrostatic Pressure- psi

Php- Hydrostatic Pressure for Proppant Added- psi/100 ft

Pisi- Instantaneous Shut-in Pressure (ISIP)- psi

PP- Pounds of Proppant- lb

psi- Pound Per Square Inch- psi

Pw- Wellhead Pressure- psi

q- Production Rate- -

qi- Injection Rate- bbl/min.

Q- Flow Rate- cc/min.

r’- Effective Wellbore Radius- ft

R- Rate- bbl/min.

RF- Rate Factor- -

SPF- Shots (perforations) Per Foot- -

TFCF- Turbulent Flow Correction Factor-Density- -

- (not used for laminar flow)

Ts- Temperature at Surface- Deg. F

u- Proppant Settling Velocity- ft/sec


82 HRD Standards

- Poisson’s Ratio- -

wf, w- Fracture Width- inch

GAC- Gelling Agent Concentration- lb/M gal

Fracture Half Length- ft

P- Fracture Friction Pressure- psi

t- Pumping Time- min

H- Fracture Height- ft

KB- Bulk Modulus- psi

cb- Compressibility- 1/psi

cf- Pore Volume Compressibility- 1/psi

- Biot’s Constant- -

cm- Rock Matrix Compressibility- 1/psi

t- Tensile Strength- psi

c- Compressive Strength- psi

BHN- Brinnel Hardness- kg/mm²

z- Stress Due to Overburden- psi

x- Horizontal Stress (minimum)- psi

y- Horizontal Stress (maximum)- psi

KIc- Fracture Toughness- psi in.

- Bulk Density- lb/ft³

rr- Radial Stress- psi

- Tangential Stress- psi

o- Shear Stress on Plane- psi

w- Average Fracture Width- in.

Wmax- Maximum Fracture Width- in.

R- Radius of Penny Shaped Fracture- ft

Definitions supplied by Damon Phillips. Compiled by Bea Hooper.

Latest Revision Date:- Mon Nov 25, 1991

Documents

Glossary of Oilfield Terms